HEPA and VOC Air Purifiers: A Doctor’s Guide
The best air purifiers combine true HEPA filtration for particles like PM2.5 with enough activated carbon to actually remove VOCs, since particles aren't the only indoor air pollution issue and VOCs are what make indoor air 2-5x more polluted than outdoor air. But air purifier marketing often takes advantage of air's invisibility, and is full of overstated claims. I evaluate every purifier on three axes: documented particle removal, VOC removal, and do no harm, since a good purifier shouldn't add pollutants back into your air (some do). See my full methodology for how they’re rated and ranked.
By Dr. Meg Christensen | Physician-founder of Interior Medicine, a non-toxic home resource built on her background in medicine, biochemistry, epidemiology, and clinical research.
Updated August 22, 2026
Air Doctor: Best Air Purifier Overall
Air Doctor is the best air purifier brand for three reasons: they’re excellent at removing both PM 2.5 and (!) VOCs, and don’t have any harmful add-ons. This is a tricky balance to strike: most are really good at only one or the other, or have harmful tech. They also make the selection process really clear: the higher in series number you go, the more VOC filtration, PM 2.5 removal efficiency, and quieter they get, so choose the best air purifier for you based on price point and room size. With their 1000 series, there’s 0.6 pounds of VOC-removing carbon, 1.5 pounds in the 3500, and 3.8 pounds in the 5500, which also has two sets of the carbon-potassium filters (the potassium has the added benefit of being able to remove formaldehyde). Likewise, the CADR (ability to catch particles like PM 2.5) increases with the series number and they have third party testing through Intertek which tests using the AHAM standard. The 3500 has a smoke CADR of 340 CFM and the 5500 at 556 CFM. They’re quiet and dark, too. For most people in most situations, these are the best air purifiers for home, striking the best balance between ease, cost and what they’re capable of. The ratings below are for the 5500; the 3500 would score High instead of Highest for Particle and VOC Removal, a combination still better than the vast majority of air purifiers out there. Use WILDFIRE10 for 10% off now.
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Medify: Best Air Purifier for Smoke
Medify does the absolute best in third party testing for particle removal, with their models consistently landing at the top of the AHAM Verifide list of 699 air purifiers for ability to clean large room sizes. They also land at the top for Smoke CADR, making them the best air purifiers for smoke. Part of this is partly due to the fact that all of their models use high quality true HEPA H13 filters. They also all contain activated carbon for capturing VOCs, though only the MA-112 and larger sizes have the more substantial carbon pellets (the smaller models just use a cloth or composite, which aren’t as effective.) They wouldn’t tell me how many pounds are in each model, though they state “substantial” carbon is present and photos indicate around 1 pound, based on similar structure to other brands that do disclose. Their MA 112 is their best air purifier for homes; their larger MA-1400 unit is part of their very effective 1000 series but covers more of a warehouse sized house. FYI, when comparing brands, note that Medify is humble in its description of the size of particles it removes. Like any other air purifier with a true HEPA filter, it can actually remove particles 10-100x smaller than 0.3 microns, not just “down to” 0.3 (read my guide below about why). They are UL certified to not generate ozone, and are quiet, with their decibel ratings listed at each fan speed. Medify accepts HSA/FSA. Get $15 off with code INTMED15.
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IQAir Air Purifier Review
IQAir has three standout air purifiers: the HealthPro, their new low plastic medical grade air purifier, and their whole-house air purifier. The HealthPro Plus XE is best at removing VOCs, but does remove PM 2.5 relatively well, too. Based on several independent testing outlets, their CADR likely falls between 200-300 CFM, though they don’t have AHAM results, likely because their focus is VOC removal and really, really thorough HEPA filtration. A note that when there’s that much media, air flow is harder to get through and the room takes longer to clean, which is likely why their CADR isn’t as high as others. That said, these have 5 pounds of carbon and potassium VOC filtration media that can even remove formaldehyde: impressive. Second, their low-plastic air purifier pictured above, the Atem Earth, doesn’t have independent testing for CADR, but it does contain 2 pounds of activated carbon and is made of beechwood. If VOC capture and less plastic usage are important to you, this could be a good option. Finally, their PerfectPro whole house air purifier legitimately works to remove PM 2.5 from your entire house with third party testing by Intertek. This won’t capture gases but paired with a dedicated VOC purifier would be the most effective way to keep your entire home’s indoor air very, very clean. It’s an investment, but fits within your existing HVAC. Ratings below are for the HealthPro Plus XE. The Atem Earth would very likely have slightly lower ratings for VOC and Particle removal; the whole-house purifier would very likely have the highest Particle removal rating but no VOC removal.
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Windmill Air Purifier Review
Windmill offers two great air purifiers. Their Max, pictured above, contains an H13 HEPA filter, and is third party tested by AHAM to have a smoke CADR of 286. It also has 0.3 pounds of carbon for VOC filtration, which is nice to see in an air purifier that removes smoke and particles so well. And, they don’t add any harmful tech. They run at 47dB on medium speed, so they’re quiet, and have an auto-fade feature so there’s no blue light at night. These do use an app for programming, but you can use it to select white noise if you’re using this in a bedroom doubling as an air purifier – white noise machine combo. You can also automate a schedule with it to save energy while you’re not home or using it. Their bamboo option blends in well as a side table, which is always a nice motivator if you’re hesitant to get an air purifier that clutters your space or doesn’t look good. Their smaller air purifiers are not as powerful, but are truly good for small rooms, with a smoke CADR of 130. For VOC filtration, these smaller purifiers have a carbon pad, which won’t do heavy duty VOC removal but will help with some basic deodorizing. Overall, they get all the basics right with nice added options. As always, just pay attention to their CADR specs and use the regular size in small rooms like the nursery or bedroom, and the Max in larger ones like living rooms or rooms needing heavy VOC removal like a kitchen. 10% off with code INTMED.
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Blueair Air Purifier Review
BlueAir has solid test data and innovative designs like purifier-humidifier combos, purifiers that double as attractive side tables or even pet beds, and even sunrise alarm clocks that purify your air. They participate in third party testing, ranking well on AHAM Verifide with good CADRs showing they’re capable of removing smoke, pollen, and dust. They use their own “HEPASilent” filters instead of standard true HEPA filters, so I was initially very skeptical they’d work, but unlike the majority of gimmicky “HEPA alternatives,” they proved theirs worked with that AHAM testing. The Blue Signature is the best air purifier they offer, rated below. These rank highest of all their models for particle removal, and well above many air purifier brands, too. These have optional legs and a flat top so you can easily turn one into a side table. One of the layers is “OdorFence,” made of a proprietary mixture of “minerals and enzymes.” This is likely safe and mostly just minerals, as enzymes need water to work, and minerals are very good at removing odors (like the potassium and zeolite disclosed in other purifiers.) Their 211, 311, and 511 are their basic models, similar in efficacy depending on your room size. Without disclosure of what the custom filters for these models are made of, coated in, or how well they work, I’d recommend sticking with their basic set, relying on their good CADR tests instead. In short, it’s hard to tell how well any of their machines remove VOCs, but these are fantastic at removing particles, and work well in daily life. Check prices on BlueAir or Amazon.
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Austin Air Purifier Review
I personally bought and tested the Austin Air Health Mate because it’s hands-down the best air purifier for VOC removal due to its 15 lbs of activated carbon-zeolite, which is even better than regular activated carbon because it can remove formaldehyde. I chose it because VOCs are elevated daily and year round in my home, while particles like PM 2.5 tend to spike during cooking and wildfires. I also like that it’s made with steel instead of plastic, and you only have to change the filter every 5 years. Last, I love how simple it is without WiFi, blue lights, or gimmicky tech. It isn’t as fast at removing PM 2.5 as some of the other machines here, because their focus is on VOC removal, but it still works moderately well at that. They don’t have AHAM testing for that CADR, but independent outlets estimate it has a CADR of around 150 (not the 400 number that some blogs cite; that’s CFM, not CADR! CADR measures clean air, not general air flow.) These do have clinical research by Johns Hopkins and a handful of other research hospitals showing they can effectively remove gases, including nitrogen dioxide (NO2) which is produced by gas stoves and heaters. I pair it with my exhaust fan every time I cook and a heavy duty PM 2.5-capturing air purifier during wildfire smoke days a couple times per year.
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Dyson Air Purifier Review
Are Dyson air purifiers worth it? My long-time critical skepticism of Dyson’s air purifiers has recently softened. Independent outlets have consistently found that most of their air purifiers have low estimated CADRs, and there is much discourse on the internet about how Dyson’s in-house POLAR testing compares with CADR testing. There are valid points on both sides, though I generally always side with third party tests being more trustworthy and having less conflict of interest. (Or I think: just own it, particles aren’t the only thing that matters!) However, their newer Big+Quiet line has performed well in independent outlet testing, averaging around 150–200 CFM for their smoke CADR. Particle-wise, that’s great news. The other hurdle is understanding whether their extra tech is harmful. They use Selective Catalytic Oxidation to destroy formaldehyde. Luckily, this is very different than PCO, and doesn’t generate harmful byproducts. There is real long-term research showing it can completely convert formaldehyde into CO2 and water. Likewise, their K-Carbon (K₂CO₃-impregnated carbon) also has research showing it can convert NOx gases into salt. NO2 is very hard for even activated carbon to capture and is a very common indoor pollutant in homes with gas stoves and natural gas heating. They did do some testing on this (GB/T 18801-2022) to confirm it works which I appreciate. All in all, if you want to capture a wide range of gases, the BP04 can be a good option. (The BP03 doesn’t have the same K₂CO₃, and the BP06 is made for commercial spaces.) Their other machines add benefits like cooling and heating, but just don’t expect a super high particle capture rate.
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Levoit: Best Affordable Air Purifiers
Levoit makes the most affordable air purifiers. They do really well in third party testing; many score highest for particle removal with impressive smoke CADRs (as verified in the AHAM directory here.) They score this well with HEPA-like filters rather than true HEPA, which makes that third party testing essential. Their new Eleva 300X does contain a true HEPA filter, and has substantial activated carbon filter options, too, which is why I use it in my office. The “essential” activated carbon filter contains 0.1 pounds, the pet one contains around 0.4, and the premium about 0.6, which is quite impressive for such a small machine. The Eleva 300X is very quiet, has a dark sleep mode, and has a built-in air quality sensor. You can use an app to control it and set up schedules, though it’s not required. The Eleva 300X also doesn’t have a Prop 65 warning. I get this question about Levoit a lot: many of their product pages have a blanket warning for Prop 65. You can read my thorough Prop 65 Guide here about why I’m generally not worried about it for an air purifier. My best guess is that there is lead solder deep in the electrical components inside some of the machines. Since it’s something I’ll never be exposed to, lead isn’t present near the filtration component, and even if it were, lead can’t volatilize into air, I treat this is one of those cases where Prop 65 adds more confusion than helpfulness. Again, enjoy the deep dive in my guide. Ratings below are for the Eleva 300X since it’s what I can attest to and is under $130 (at the time of publishing) but note that many of their machines have much higher CADRs, which you can see in the AHAM directory. Check prices on Amazon or their website.
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Coway Air Purifier Review
Coway makes four very similar models of Airmega Mighty purifiers that do very well in particle removal testing and are priced between $239-$299, making them a favorite among many review sites. This includes the AP-1512HH, AP-1512HHS, Mighty2, and the 200M. (FYI, the AP-1512HH and the 200M are confusingly the exact same model in terms of performance, just with a different aesthetic.) All have smoke CADRs between 210-240, making the biggest difference between them from a health standpoint how much VOC filtration media they include. The HHS has the most, with 0.35 pounds of activated carbon pellets in a honeycomb-style filter. The others use carbon-coated HEPA filters or separate carbon pads, which provide light deodorization, but not nearly as much VOC removal as pellets do. The trade-off for the better VOC filtration in the HHS is the lower CADR (210) and higher price point ($299) of the bunch, though both of those stats are still very good compared to the vast majority of purifiers out there. I honestly think all four of these are good choices that will work for a very long time, look nice at home, and run quiet and dark. These all contain an optional ionizer, though all are CARB certified so won’t add ozone to your space. Each offers a different set of conveniences, whether you want to use an app, save $60, have a certain look, or have the best VOC filtration. Their larger, more expensive models outside of the Airmega line also have good CADRs, though have less carbon than other brands for the same price, so their Mighty/200M line is what I’d recommend focusing on! (I bought the original AP-1512HH in 2018 and it’s still running very well today.) Check prices on their site or through Amazon.
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sans Air Purifier Review
The sans air purifier has a handful of good things going for it: it's very pretty, very quiet, and has more carbon VOC filtration than most air purifiers on the market, with 1 lb of activated charcoal. It does have a true H13 HEPA filter, which is nice, too. However, they don't share independent third party testing of how well it works to capture particles. You want to know that the air is actually going through the H13, not around it, and, on the other hand, that it's not so tight it never gets a chance to clean the whole room. They state an in-house CADR of 420 m³/hr but that's a little tricky: AHAM and other purifiers use cubic feet per minute, not cubic meters, so this is actually a CADR of 247. They have a UV-C light that's CARB certified to not produce ozone, which is good. All in all, I think these look nice and if you trust their in-house numbers, are very effective. If they shared independent third party test data that matched their claims, they'd jump up very high on my list.
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Corsi-Rosenthal Box DIY Air Purifier Review
You can build a DIY air purifier out of HVAC filters, tape, and a fan. They’re not pretty, and don’t have activated charcoal or any useful tech, but they do work better at capturing particles including smoke better than some of the air purifiers on this page! The Corsi Rosenthal box uses five MERV 13 filters and one fan to create a cube. It draws room air in through the filters and the fan pushes cleaner air out. This set up has been tested by the Illinois Institute of Technology’s Built Environment Research Group and found a smoke CADR of 168, though the number varies widely between testing set ups, from 80 all the way up to 330 with a powerful fan. The single filter and single fan set up also works, though less effectively than the 5-sided filter does. You can build one yourself. Use these instructions, valid MERV 13 filters, tape, and a Lasko box fan (the reputable brands recommended by the original Corsi-Rosenthal Foundation.)
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Winix Air Purifier Review
Winix offers a variety of air purifiers, with their 5510 being the most popular because it was one of the most affordable air purifiers that has truly good particle filtration. Unfortunately, none of their currently available purifiers strike the balance between excellent particle filtration and VOC filtration for odors, gases, and smoke smells any longer. The 5510 is replaced by the 5520 and is AHAM Verifide rated, which I always appreciate, since you can see a third party has tested it for effectiveness: its Smoke CADR (the hardest size of particle to capture) is 253. But, you can only get the carbon cloths instead of the pellets for VOC filtration. That’s fine if you’re not interested in gas or odor removal, and it’s quiet under 50dB at medium speed. It does have “PlasmaWave” ionization (generates <0.01ppm ozone, which is technically safe but also unnecessary.) I recommend keeping it off though its default is switched on and you have to turn it off every time you turn the air purifier on.
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Dayette Air Purifier Review
I was asked to review Dayette and found it very interesting. They look amazing: they have two H14 medical grade HEPA filters and are very cheap. That immediately made me wonder if they're too good to be true, so did a deep dive. Zhongshan Scien Top Appliance Co., Ltd. makes them, and also sells the same models under a few other brand names like Smile Air, Dr. J Professional, JOWSET, and Ruwora. (You can find out by looking up the brand name in CARB's directory, then cross-referencing the EO number.) They have CARB certification for not producing ozone or ions, which is good, but no testing for effectiveness. The CADR numbers on the same air purifier models change from site to site depending on the white label brand they're sold as, and they don't have any third party testing to prove that the CADR numbers are real. I also wouldn't put a lot of stock into the five star reviews on Amazon; they have a free filter deal attached to giving them a star rating on their website, which may influence those ratings. That's important because a HEPA H14 medical grade filter is woven very tightly (standard is H12 or H13). This sounds good on the surface, but aren't used often because air has a hard time getting through them efficiently without a very powerful fan. It's loud, between 50-80dB on any speed above its lowest sleep mode setting. Without third party CADR numbers, some air may escape through the sides and not get cleaned. Bottom line: I don't know if these work and there's no way to tell. I'd be cautious given air purifier scams. I'd go for a Levoit instead, which are similarly inexpensive and have data to confirm they work.
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Air Oasis Air Purifier Review
Air Oasis seem to have the basics down, but unfortunately, they add tech that may be harmful. They have substantial amounts of activated carbon VOC filtration in their units, which is also a good thing: 0.6 pounds in the medium and 1.2 pounds in the Pro. They use true H13 HEPA filters and have theoretically high CADRs, but these are not Intertek or AHAM tested, and they use a general CADR rather than a smoke-specific one. I’m not confident they’re as high as they claim, so without raw data or a named lab, they get a Low rating for this. And while I get the temptation to do something different or differentiate yourself in a crowded market, they use two pieces of tech that I’m very cautious about: PCO (photocatalytic oxidation) and UVGI (UV germicidal irradiation) both of which can generate formaldehyde or acetaldehyde and other incomplete breakdown products of VOCs. I appreciate that they are CARB certified to not generate ozone, making their ionizer less of an issue, but for me, the possibility the other two pieces of tech present is a dealbreaker. I understand they are appealing to mold and mycotoxin issues, but any of the air purifiers with a true HEPA filter, good CADRs, and substantial VOC adsorbent will take care of mold spores, mycotoxins, and gases without the extra risk. If they can show third party testing that demonstrates no aldehydes are created, I’d be comforted.
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Intellipure Air Purifier Review
Are Intellipure air purifiers good? It’s murky. I was initially excited by their H1000 model because it has an H13 HEPA filter and two large honeycomb style activated carbon filters. I hoped this meant a high CADR and VOC capture, but needed to know if it was built appropriately to actually push air through those heavy duty filters effectively without leaking through gaps or being excessively loud. As I asked questions about performance, it took me down quite a deep rabbit hole. Healthway creates air purifiers that they distribute under the names Intellipure and Pure Wellness, often resold by Delos Living, and are mostly marketed toward commercial spaces like school and hotel rooms. Their Compact air purifiers were purchased by New York City schools during COVID and later found to be very loud and only have a smoke CADR of 129. Their new model looks promising and they emailed me CADRs, but none were for smoke, citing only a general number and a “third party lab” without disclosing what lab it was or what the results were. Given their past history, I am not sure I’d trust that this model works better than the Compacts. No reputable independent outlets with consistent systems have tested it either. If I can see true smoke CADR results, I’d be convinced. They also told me that the total carbon weight was “less than 1 pound” without giving me a clear number. Getting information from the website or via email was difficult and sparse. At $400+, with poor past performance history, I’d opt for a different air purifier.
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Canopy Air Purifier Review
What Canopy’s Bedside Air Purifier lacks in power, it makes up for in thoughtful and convenient design. First, the air purifying facts: they use a true H13 HEPA filter, which is great, but it’s such a tiny machine, its smoke CADR is the lowest on this entire page: 45 CFM! Their air purifiers do also contain activated carbon, but just in the form of a pad. It’s likely doing some light deodorizing work, but not protecting you from VOCs during a wildfire or any new furniture or new building off-gassing. That said, if you have a small bedroom that a tiny air purifier can handle coverage-wise, they get a lot else right. It goes totally dark and quiet on its own at night, and its loudest speed is still under 50dB. There’s no ionizer, UVGI or other potentially harmful tech. It’s app-free if you like a phone-free bedroom, has an evening wind-down night light and white noise option, and is small and light enough for traveling. I’d recommend against adding their optional aromatherapy, which adds VOCs to your space, negating the carbon pads’ purpose. If you are like, “too bad, Interior Medicine, I love scent and you can’t take it away from me”, just consider using your own 100% organic one, and know that their scents are a blend of natural and synthetic substances.
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FYI, “non-toxic” has no official definition, so I rate every product with the same method. It’s built on third-party certifications and published test data, not brand claims. For a deeper dive, my free course walks you through it.
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More Healthy Design For You
How Interior Medicine Rates Air Purifiers
For air purifiers, I rate on particle removal, VOC removal, and lack of harm, using the Health Function Scale, one part of my consistent rating Methodology. It runs from highest to lowest. Air purifiers have three separate ratings because they can vary wildly on their ability to remove particles like PM 2.5 and VOCs. Many rely on marketing that adds harmful gimmicks, so that's included in the ratings, too:
Particle Removal
Particle removal effectiveness is based on third party test results for smoke removal because that is the size range that includes the hardest particles to capture. AHAM has the most rigorous and consistent testing rules, so I use their standards. CADR, or Clean Air Delivery Rate, is the best way to compare air purifiers side by side because it measures how much clean air actually comes out. That takes three things working together: a good HEPA filter, a fan strong enough to push air through it, and a housing sealed well enough that air can’t slip around the filter. A great filter in a leaky machine still scores low. CADR is tested on the highest fan setting, so that’s the number I use.
TIER 01
Highest
What qualifies
ANSI/AHAM AC‑1 smoke CADR of 500 or above.AHAM smoke CADR 500+
Evidence / Info
AHAM certifies smoke CADRs from 10 up to 600. If you see ">600," the machine tested higher than AHAM can certify. Their testing is trustworthy because they can pull random units off store shelves and retest them at any time (AHAM Directory 2023).
TIER 02
High
What qualifies
ANSI/AHAM AC‑1 smoke CADR of 250 or above. Or, has met an equivalent, like a PM1 CADR of 250 or above through an independent testing outlet that publishes its testing room size and raw data.Smoke or PM1 CADR 250+
TIER 03
Moderate
What qualifies
ANSI/AHAM AC‑1 smoke CADR of 150 or above. Or, has met an equivalent, like a PM1 CADR of 150 or above through an independent testing outlet that publishes its testing room size and raw data.Smoke or PM1 CADR 150+
TIER 04
Low
What qualifies
Verified performance below the Moderate bar, or no third party performance data.Under 150, or untested
TIER 05
Lowest
What qualifies
Performance claims rest on unverifiable or pseudoscientific technology (water, moss, PECO, probiotic, etc.) with no verified particle data.Unverifiable technology
VOC Removal
VOCs can effectively be removed from air by adsorptive filtration materials like activated carbon, potassium permanganate, or zeolite. Effectiveness is measured in pounds because these materials work by surface area. A single pound of activated carbon holds roughly 85 football fields of surface folded into its pores. More pounds means more surface, which means more molecules held and longer before it saturates.
TIER 01
Highest
What qualifies
Contains 5 or more pounds of activated carbon, zeolite, or similar adsorptive media.5+ lb adsorptive media
Evidence / Info
Adsorbent filters only work well when they hold enough media for the job, and more media works longer (EPA 2018).
TIER 02
High
What qualifies
Contains 1 pound or more of carbon or similar adsorptive media.1+ lb adsorptive media
Evidence / Info
Adsorbents have a finite capacity and need regular replacement (EPA 2018).
TIER 03
Moderate
What qualifies
Contains 0.5 to less than 1 pound of carbon or similar adsorptive media.0.5 to under 1 lb
TIER 04
Low
What qualifies
Less than 0.5 pounds of carbon or similar adsorptive media (including carbon-coated fabric or composite carbon).Under 0.5 lb, cloth, or coating
Evidence / Info
Carbon spread in a thin layer saturates quickly and can release what it trapped back into the room. These filters have a short service life and usually do little for odors (EPA 2018).
TIER 05
Lowest
What qualifies
No carbon or other adsorptive media.None
Do No Harm
Some air purifiers add technology beyond filtration (like ionization, UV light, or photocatalysts like PCO) to differentiate themselves. Innovation is important, but each of these puts something into your air, which carries risk. Ozone irritates and damages lung tissue. Photocatalysts can partially break down VOCs into formaldehyde and acetaldehyde. Read more in the FAQ below about each of these. Finally, bright blue indicator lights can disrupt sleep, and a loud purifier can disrupt you too.
TIER 01
Highest
What qualifies
Cleans by filtration alone. No photocatalyst. No ionizer, bipolar ionization, or plasma. No germicidal UV. No blue or indicator light at night, or it can be dimmed or turned off. Under 50 dB at medium fan speed.Filtration only, quiet, dark
Evidence / Info
Noise is one of the main reasons people turn air cleaners down or off. CADR ratings are measured at maximum airflow, which is usually the loudest setting (EPA 2018).
TIER 02
High
What qualifies
A small imperfection. The indicator light can't be turned off, or it runs above 50 dB at medium fan speed. Or, includes a potentially harmful emitting technology, but the risk is optional and ozone output is verified as low or essentially none. This would be like an ionizer or germicidal UV that is CARB listed or UL 2998 verified, fully enclosed within the unit if UV, and can be switched off completely. No photocatalyst (like PCO or PECO).Optional, ozone-verified tech
TIER 04
Low
What qualifies
Includes an ozone-emitting technology that you can't opt out of. An ionizer or enclosed germicidal UV that is ozone-verified but runs whenever the machine runs, with no way to disable it.Always-on emitting tech
Evidence / Info
In a randomized crossover study of 56 college students, negative ion purifiers lowered indoor PM2.5. Ion exposure raised a urinary marker of oxidative stress enough to cancel out that benefit (Indoor Air 2021).
TIER 05
Lowest
What qualifies
Uses a photocatalyst (PCO, PECO, or any branded variant), which can produce formaldehyde and acetaldehyde from incomplete VOC breakdown. Or germicidal UV that emits into the room rather than staying enclosed, or uses an ozone-generating wavelength. Or an ionizer or plasma generator with no CARB listing or UL 2998 verification.PCO, open UV, or unverified ionizer
Evidence / Info
NIST (the National Institute of Standards and Technology) tested air cleaners using seven technologies in a test chamber. The PCO and germicidal UV units produced the most aldehyde byproducts, at 202 and 243 micrograms per hour (NIST 2024). Uncoated UV-C lamps at 254 nm and below can also generate ozone (EPA 2018).
I use these scales to rate by brand first, then name specific units worth considering in the description. Different air purifier models can vary widely in terms of effectiveness within one brand, however, most companies do have the same underlying architecture and testing that's consistent across all of their models. For example, some brands will use H13 HEPA filters for every single unit, some will have AHAM CADR testing done for every single model, some will forgo that type of testing entirely as company policy. I call out which model the ratings apply to, and make note of differences among other relevant models in the description.
Evidence gaps
No certified VOC rating exists yet. AHAM published a chemical removal test method, AC-4-2022, but says a chemical CADR will only eventually be added to its certification program (AHAM 2025). Until then, pounds of media show capacity, not a measured removal rate. Plain activated carbon is also weak against formaldehyde. Chemisorbent media, like potassium permanganate, does better because it reacts with gases and traps them permanently (EPA 2018).
CADR is measured at the highest fan speed, and most people run purifiers lower (AHAM 2020).
Air Purifiers Explained: Your Complete Guide to HEPA, VOCs, Certifications & What Actually Works
Table of Contents
How do air purifiers work? A visual explanation of the three filter types and air flow through them
What good air purifiers can actually remove: a chart of particles and gases
Air purifier logistics: how many to get and where to place them
Why Interior Medicine is the Best Air Purifier Review Website
What are the best air purifier reviews?
Interior Medicine has the best air purifier reviews because they’re based on certifications, unbiased data, and cover all three important aspects of an effective air purifier: particulate removal, VOC removal, and the lack of harmful additives like ozone generation. My recommendations for the best air purifiers for your health are listed above.
Air purifiers are an unregulated industry. High performance is easy for brands to claim, because air and its contaminants are invisible to human detection. Performance is complicated and expensive to measure, so it’s difficult for regular people at home to check whether their air purifier really works. And, the specs are hard for most people to interpret before buying one, too. (Jump down to see how CFM, CADR, and ACH are different, for example.)
AHAM Verifide is the only third-party testing standard in the US, and it's voluntary.
All of this means that air purifier reviews are an important part of understanding which ones work. But, there are three problems to keep an eye on when reading air purifier reviews:
Potential Earnings Bias: The majority of air purifier reviews and round-ups are based on anecdotes, ease-of-use, budget, aesthetics, and sometimes potential for affiliate commission. These are common in lifestyle magazines and wellness blogs, for example. This can lead to air purifier recommendations for machines that don’t actually work, or even have harmful technologies (ozone generation, for example). While of course some of these things (like budget and ease of use) are absolutely practical, these review methods are very susceptible to bias. When someone reviews an air purifier they get a good commission for, they may be subconsciously (or consciously, without shame!) more likely to rate it higher than it deserves. If they show exactly what their system for rating is, demonstrate a solid understanding of air purifier mechanics and indoor air quality, and demonstrate ways they remove bias, that’s a good sign, but this is something to be aware of as you look for the best air purifier.
Testing Quality: The reviews done by independent testing outlets for air purifiers are generally much better than lifestyle blogs. They typically rely on particle counters and consistent methods. But, they’re still not as reliable as a big lab with ultra-accurate equipment, the ability to produce the exact same amount of particles to test every time, and ability to test what’s called “natural decay.” The room size is often smaller in independent outlets, too. This can mean you don’t get a real-life version of how the air purifier would perform in your house, in a normal-sized room. An air purifier capable of reducing all the particles in a 90 square foot room in 30 minutes is not very impressive once you move it to a larger room. Finally, independent outlets generally test a brand’s machine that was sent specifically to them just once. It doesn’t include the random testing on models throughout the year that AHAM does. Outlets that publish their methods, room size, and raw data for particle reduction are doing a great job, but it’s important to know the limitations. AHAM gives you the most unbiased information and most accurate lab results.
No VOC Removal Focus: AHAM and independent testing outlets only focus on particle removal. Particles are easier to measure than VOCs, which is likely why. However, in 2018, a study showing VOCs contributed as much to outdoor air pollution as vehicle exhaust. Lotions, paints, perfumes, household cleaning products, and human breath and activity contribute as much to air pollution as cars. Indoor VOC concentrations are often 10 times higher than outdoor concentrations, and as new homes are built tighter and for more energy efficiency, ventilation is dropping. Wildfires that burn structures and homes release VOCs including formaldehyde and polycyclic hydrocarbons from paints, plastics, sealants, insulation, and treated wood. VOCs are related to negative health outcomes (read more below) and VOC removal should be considered in air purifier ratings.
Placebo Effect: Consumers reviewing the air purifiers they bought online with star ratings may be basing it party on the placebo effect. If someone spends time and money on something, it can make them feel like their air is cleaner even when it isn’t. This has happened in real life: the $800+ Molekule had great reviews before it was discovered through testing to be one of the least effective air purifiers on the market. Its PECO technology is also known to generate formaldehyde from incomplete breakdown of VOCs, possibly creating more problems than it solved. It was expensive, aesthetically pleasing, and had great marketing that sounded better than HEPA…but it didn’t work at all. (They retracted their claims and added a regular HEPA filter to their machines.) Human experience just isn’t super reliable when it comes to detecting air quality specifics.
Are there any 3rd party certifications for air purifiers?
Very few, and they are voluntary.
CARB (the California Air Resources Board) and UL (Underwriters Laboratories): these are third parties that verify that air purifiers don’t generate ozone.
AHAM Verifide: The Association of Home Appliance Manufacturers (AHAM) standardized the clean air delivery rate (CADR). This measures how well an air purifier can remove dust, pollen or tobacco smoke fro the air and is the best certification we have for air purifiers so far, because it is a true third party testing group. It doesn’t measure the removal of VOCs.
HEPA: HEPA is not actually a 3rd party certification, but legally, a company can only say their filter is a HEPA filter if that is indeed true. A HEPA filter doesn’t always mean a certain number of particles are captured; air flow needs to be considered too. A filter needs to be secured and air tight to ensure all air passing through it is actually filtered.
Do air purifiers actually work?
Do air purifiers work?
Yes. Air purifiers with true HEPA filters, good air flow stats, and third party testing work. They can both improve your health and the health of your home.
Indoor air is 2-5 times more polluted than outdoor air, even if you can’t smell or see how bad it is. Air purifiers reduce your indoor air pollution by removing Particulate Matter (like wildfire smoke, mold spores, and pollen.) Air purifiers with adsorbents can also remove VOCs (like formaldehyde). Lowering your daily exposure to particulate matter and harmful VOCs can help reduce your risk of long-term health problems.
Are air purifiers worth it?
Yes, absolutely. If you’re like most people, you spend around 90% of your time indoors, and a lot of that at home. While you can’t control the outdoor air quality, you can control your indoor air quality. As long as you choose one that actually works, an air purifier is one of the best investments for your overall health.
As wildfire smoke and poor outdoor air quality become more common, an air purifier that removes dangerous PM 2.5 and VOCs from smoke can protect not only your lungs but your whole body. Ultra-fine particles are able to cross through the surface of the lungs and into your bloodstream, which is one of the reasons why PM 2.5 exposure is related to inflammatory, chronic conditions.
Why is it hard to find a good air purifier?
Air Purifiers are high tech, expensive, increasingly important for people to have, and work on an invisible level. Unfortunately, this creates a perfect storm for healthwashing, and the number of air purifier companies making false claims to trick customers into thinking they’re buying a superior product has been well-documented as a problem.
How to choose the best air purifier for your home
These are the three most important things to look for:
A high smoke CADR: Clean Air Delivery Rate (CADR) is the most important thing to look for, because it's a consistent number you can use side by side between air purifiers. It lets you rank units against each other, unlike "suggested room size," which is a marketing number, or CFM, which measures how much air the fan moves rather than how much air actually gets cleaned. Higher is better. It's a measure of how quickly an air purifier is able to actually pull particles out of the air, which usually means a strong fan paired with a filter that's well-positioned and sealed around the edges so air can't leak past it. Smoke is the smallest size range where filters struggle most, so a high smoke CADR is the most impressive number for particle removal.
A VOC filter filled with activated carbon pellets. This is what captures VOCs from the air, like cooking odors, new-building off-gassing, and smoke smells. The pellets are better at doing this than carbon cloth or deodorizing pads because they have so much more surface area to trap VOCs within. I’m impressed with how many brands are finally adding these to their units! Air purifiers have traditionally only focused on particle removal, which is what HEPA filters do. But in 2018, VOCs from household products officially became 50% of outdoor air pollution, sharing the space evenly with car exhaust particles. They’re finally getting a little more of the attention they deserve. For this, focus on how many grams or pounds the filter has: more is better for VOC removal.
Do No Harm: fancy tech is often added to air purifiers by brands trying to differentiate themselves in a crowded space. Sometimes that innovation is great! I'm genuinely impressed with some of the ideas that have evolved, like wool and plant-based filtration material, pet bed shaped purifiers, and others. But, sometimes it backfires: PCO technology in air purifiers actually create formaldehyde and acetaldehyde as byproducts of incomplete VOC breakdown, in some cases leaving the air with more of both than it started with. In terms of tech, stick with the basics (HEPA and carbon) until we know more.
See how well common air purifier brands meet all three criteria and compare them side by side at the top of this page.
How Do Air Purifiers Work?
Air purifiers work using a combination of filters and generating good air flow intake that forces dirty air through those filters:
First, the filters. Air purifiers generally use a three-stage filtration system to remove three different types of pollutants from indoor air.
Stage 1: Pre-Filter (Captures Large Particles)
The pre-filter is the first line of defense, capturing large airborne particles including:
Pollen and allergens
Pet hair and pet dander
Dust (including larger dust mite particles)
What to look for: If you need an air purifier for allergies, pets, or dust removal, prioritize an air purifier with a large washable, reusable pre-filter to reduce long-term maintenance costs. Regular cleaning (every 2 weeks) keeps your air purifier running efficiently.
Stage 2: True HEPA Filter (Removes 99.97% of Microscopic Particles)
A true HEPA filter (High-Efficiency Particulate Air filter) captures small particles, including:
Wildfire smoke particles
Mold spores and mycotoxins
Dust mite allergens and feces
Bacteria and some viruses
Other fine particulate matter (PM 2.5)
Important fact: to be called a true HEPA filter, it must meet strict standards, and be able to remove 99.97% of particles 0.3 microns in size, as well as particles much larger and smaller. This is the gold standard for air purification and this is the most important part of an air purifier, because we have so much research showing how PM 2.5 exposure is harmful to the body. Read more below for more details on how HEPA filters work and for a visual diagram.
Stage 3: VOC Filter (Adsorbs Odors, VOCs & Gases)
The VOC filter or gas adsorbent (often an activated carbon or sometimes a mineral blend) removes gaseous pollutants too small for HEPA filters to catch, including:
Volatile organic compounds (VOCs)
Cooking odors and kitchen smells
Smoke odors from cigarettes or wildfires
Formaldehyde from new furniture, carpets, and building materials
Chemical fumes and off-gassing from paint or cleaning products
Not every air purifier has this layer. These are less common than HEPA filters, and often are minimal, just a carbon cloth. Substantial adsorbent filters can contain up to 15 pounds of carbon, zeolite, or other mineral blends that are capable of sequestering formaldehyde and other gases. Read more below to see how adsorbent works and for a visual diagram.
Pre-Filters in Air Purifiers
A pre-filter is the first stage of filtration. It’s usually a coarse mesh or fabric screen sitting in front of both the HEPA and VOC filters. It catches the big, visible stuff before it reaches them, like pet hair, lint, dust bunnies, dander clumps, and larger pollen. It works by simple sieving, similar to the way a screen door works. The particles are just too big to fit through.
The pre-filter's real job isn't cleaning your air, but protecting the expensive filters behind it. A HEPA filter would capture pet hair perfectly well, but it would clog fast doing it, and HEPA filters are relatively expensive and something you have to replace. A pre-filter is cheap, and most are washable or vacuumable. That means a pre-filter mostly affects filter life and running cost, not what comes out of the machine. Vacuum it monthly, and if you rinse it, let it dry completely before it goes back in!
One thing to watch: "carbon pre-filter" is commonly marketed, and it can mean a thin carbon coating on the mesh, or a relatively thin carbon pad. These won’t do any substantial VOC removal: you need pellets on the order of pounds to do that.
What HEPA Filters Remove
The graph below shows how good HEPA filters are at capturing particles that are 0.3 microns in size, the hardest size of particle for any air filter to capture:
Bigger particles get caught by impaction and interception. Smaller ones drift into fibers by diffusion. Around 0.3 microns neither mechanism works well, so each curve dips. HEPA dips too, but its minimum is 99.97%, which at this scale is a flat line along the top.
MERV curves redrawn from the figure in Persily, A., Chapman, R., Emmerich, S., Dols, W., Davis, H., Lavappa, P., Rushing, A. (2007). Building Retrofits for Increased Protection Against Chemical and Biological Releases. NIST. Values are read off the published figure and show the shape of the relationship, not exact test results. The True HEPA line is my addition.
How does HEPA filtration work?
The graph above looks a little complicated, but if you’re interested, it’s very cool to see how HEPA filters remove 0.3 micron sized particles.
From top to bottom: the particle removal efficiency ranges from 0-100%.
Along the bottom of the graph: this shows the diameter of particles found in air, which ranges from 10 microns (the size of pollen) all the way down to 0.01 microns.
The curved lines on the graph are different MERV filters: MERV means Minimum Efficiency Reporting Value. MERV is a measure of how good an air filter is at trapping particles. You may have seen MERV 8 or 12 filters for your furnace, for example. The dip in the middle of each MERV curve happens right around 0.3 microns in particle size. Every level of MERV has a hard time capturing this size.
The nearly-flat line at the top of the graph is a true HEPA filter: for a filter to be called HEPA, it must capture 0.3 micron particles with 99.95% efficiency. HEPA filters easily capture particles 10x smaller and much larger than 0.3 microns, at about 100% efficiency.
What does HEPA mean? What is a true HEPA filter?
HEPA stands for High Efficiency Particulate Arrestance. For an air filter to be called a HEPA filter, it must be capable of removing at least 99.97% of particles that are 0.3 microns in size, like pollens, mold spores, bacteria, and others. HEPA filters easily capture particles 10x smaller and much larger than 0.3 microns, at about 100% efficiency.
Are HEPA-style or 99% HEPA filters the same as regular HEPA filters?
No! The terms HEPA-style, HEPA-like, 99% HEPA, and others, are not real HEPA filters. These do not filter particles with the same efficiency as HEPA filters, and may not filter small particles at all. HEPASilent is the exception so far; it is a more loosely woven, charged filter made by BlueAir and importantly, third party testing and its CADR numbers back up its effectiveness.
Is HyperHEPA or UltraHEPA better than regular HEPA?
No, these are marketing tactics. If you look closely, these filters are just H12, H13, or H14 HEPA filters. They all remove particles 100 times smaller than 0.3 microns— that’s the definition of HEPA. Due to complicated physics, 0.3 microns is the hardest size of particle to capture. It’s actually easier to capture particles both larger and smaller than this. Some of the brands listed above make the claim their HEPA filters are better than others, but I’ve decided not to hold it against them because their machines work really well in third party testing to protect people from dangerous particles and gasses. Big of me, I know! ;)
What is an ULPA filter?
ULPA filters are Ultra Low Penetration Air filters. They can actually capture even more particles than HEPA, but, they do not work as well as HEPA filters, because they are so tight, that air has such a hard time getting through them. They have a very low CADR (clean air delivery rate). They may appear better on first look, but they are not recommended, because they clean very small amounts of air.
True HEPA vs HEPA-Type vs ULPA Filters: what's the difference?
True HEPA: an air filter capable of removing at least 99.97% of particles that are 0.3 microns in size
HyperHEPA / UltraHEPA: usually just a true HEPA filter with marketing or branding attached. You can tell by looking at the specs, which will usually specify a standard true HEPA filter.
HEPA-Type / 99% HEPA / HEPA Style: not a real HEPA filter and not necessarily capable of capturing particles well
ULPA: ultra-low penetration air filters. Do not work as well as HEPA because so little air can get through to be cleaned.
PM2.5 vs PM10: Understanding Particulate Matter and Indoor Air Quality
What is Particulate Matter?
Particulate Matter is a fancy term for particles: tiny bits of solid or liquid floating in the air you breathe. You'll see it written as PM, and it's sorted by size (PM10, PM2.5, and PM1), because size determines how far into your body a particle can travel.
Where does particulate matter come from?
Indoors, particulate matter comes from pollen, dust, dust mite fragments, pet dander, and mold spores. It also comes from anything burning or heating: gas stoves, cooking oil, toasters, natural gas heaters, candles, fireplaces, wood stoves, and cigarettes. Sanding, sawing, and woodworking produce it too.
Outdoor sources get in through windows, doors, and ordinary gaps in the building envelope, which is how wildfire smoke, traffic exhaust, and industrial pollution end up in your living room even with everything closed.
Your body doesn't distinguish between sources. A particle from a scented candle and a particle from a wildfire are handled the same way once they're in your lungs. "Natural" sources of smoke doesn’t mean safe: wood smoke, wood dust, and even long-time exposure to cooking exhaust are all known human carcinogens.
What is PM 2.5?
PM2.5 is particulate matter smaller than 2.5 microns, which is roughly 30 times thinner than a human hair. These particles are small enough to travel past your airways, reach the deepest part of your lungs, and cross into your bloodstream. From there they circulate to your heart, your brain, and the rest of your body.
PM2.5 includes fine smoke particles, small mold spores, soot, airborne metals, and particles formed by chemical reactions of gases like sulfur dioxide (SO2) and nitrogen oxides (NOx).
Why is PM 2.5 bad?
Because it doesn't stay in your lungs. Larger particles get trapped and cleared. PM2.5 gets absorbed, and once it's in circulation it causes inflammation in tissue that never touched the air. PM 2.5 can increase the risk of heart attack and worsening of heart failure, increase ER visits, hospital admissions, and premature deaths, and is increasingly linked with dementia and Alzheimer’s Disease. It’s a major global health concern, both outdoors and indoors, and though indoor levels tend to be lower and are harder to track, can certainly be raised during daily cooking, wildfire smoke penetration through windows, burning candles regularly, and other indoor air pollution events.
What is PM10?
PM10 refers to particles below 10 microns and above 2.5 microns: pollens, molds, dust, and dust mite fragments. These are too big to reach your bloodstream, so their main effect is irritation of the throat and lungs. They can cause coughing, wheezing, and exacerbations of asthma, and reduce your lungs' ability to clear out bacteria and viruses.
Irritation can become chronic irritation, which can become inflammation, and inflammation over years is how a lot of disease starts. This is why particulate matter irritation is taken seriously for cancer risk.
What is ultrafine particulate matter?
PM0.1, or ultrafine particles, are smaller than 0.1 microns. They come from combustion, gas stoves, laser printers, and traffic. They cross into the bloodstream even more readily than PM2.5, and there's evidence they can reach the brain directly through the olfactory nerve. Most consumer air quality monitors don't measure them, and no US standard regulates them, which means they're a real exposure most people never see anything about.
How do you remove Particulate Matter from home?
With a true HEPA filter. All regular HEPA filters are capable of removing particles 100 times smaller than 0.3 microns at nearly 100% efficiency— it’s boring, but true. HEPA means High Efficiency Particulate Arrestance (or sometimes High Efficiency Particle Air).
Due to complicated physics, 0.3 microns is the hardest size of particle to capture. It's actually easier to capture particles both larger and smaller than this. So a HEPA filter removes ultrafine particles at close to 100% efficiency, which surprises people. It's boring, but true: the filter technology from the 1940s still outperforms every marketing term invented since.
Source control comes first, though. Run your range hood, use your exhaust fans that vent to the outside, don't burn things indoors, and use the HEPA to capture what’s left over.
Cooking Air Pollution: How Much PM2.5 Does Cooking Actually Create?
Cooking creates surprising levels of indoor air pollution, even when you don’t burn anything or can't see smoke.
I did a real-time air quality test: you can watch the video by clicking on the photo, or read my results here:
PM2.5 levels (fine particulate matter) spiked from 1 to 57 during normal dinner preparation (over 6 times the EPA's safe outdoor limit of 9 micrograms per cubic meter.) Simply sautéing chicken and boiling noodles generated dangerous levels of airborne particles linked to heart disease, asthma, and cancer risk. Even with a kitchen exhaust fan running on high and an open door, indoor air quality remained hazardous at 44 PM2.5 immediately after cooking. It took 30 minutes for particle levels to naturally drop back to 9, while VOCs (volatile organic compounds) remained elevated. This demonstrates why kitchen ventilation and air purifiers are essential for healthy indoor air: cooking pollution happens daily, even when your air looks clear. Running your range hood every time you cook and using a HEPA air purifier with activated carbon filtration can protect your family from these invisible cooking fumes and particulate matter.
Air Purifiers for Smoke
Is wildfire smoke particles or gas?
Both. Wildfire smoke is a mixture of particulate matter and gases. The particles are mostly PM2.5 and ultrafine, which is why smoke haze reaches your bloodstream so efficiently. The gas phase includes formaldehyde, benzene, acrolein, and carbon monoxide, produced when vegetation, homes, cars, and plastics burn.
This is why a HEPA filter alone isn't enough during a smoke event: the HEPA filter captures the particle half but no gas. You need activated carbon on the order of pounds for that.
What is the best air purifier for secondhand smoke?
The best air purifier for secondhand smoke has a true HEPA filter with an AHAM Verifide smoke CADR at least two-thirds of your room's square footage. It should also have more than 1 pound of activated carbon.
This is because tobacco smoke is a mixture of particles and gases, and an air purifier that only handles one leaves you breathing the other.
The particle half consists of fine and ultrafine particles: PM2.5 and smaller, which is why cigarette smoke reaches the bloodstream. A true HEPA captures these particles.
The gaseous half is nicotine vapor, formaldehyde, benzene, and acrolein. HEPA can’t capture these. Even something marketed as HyperHEPA or UltraHEPA that can capture particles down to 0.003 microns can’t capture these gases (scroll up to see a visual of gas vs. particle sizes.)
This is one of the few areas of air purification with real clinical evidence behind it. A double-blind randomized trial at Cincinnati Children's Hospital put HEPA purifiers with carbon (or identical sham units) in the homes of 225 children with asthma who were exposed to secondhand smoke. The children in homes with working units had 18.5% fewer unscheduled asthma visits over twelve months. A separate Johns Hopkins study in homes of pregnant women living with a smoker found significant reductions in indoor PM2.5 and in salivary cotinine, a biomarker of nicotine exposure.
Filtration reduces exposure, but isn’t a substitute for a smoke-free home. Also remember to use a fully sealed HEPA vacuum and wet dust weekly to capture any smoke particles that have settled into carpet, upholstery, or onto surfaces.
What is the best air purifier for wildfire smoke?
The best air purifier for wildfire smoke removes both particles and gasses. It should have a true HEPA filter with an AHAM Verifide smoke CADR roughly equal to your room's square footage, and at least 1 pound of activated carbon:
AHAM Verifide means the CADR was tested by a third party and they can do surprise test checks on air purifier units anytime. A CADR without AHAM Verifide may be true, but it’s harder to know if the company is being honest. To find the smoke CADR, look at the technical specs on an air purifier’s page.
Smoke CADR is the best number to use here, not the overall CADR or pollen CADR. smoke stands in for the smallest particles (0.09 to 1 micron). That's the size range wildfire smoke lives in. A unit can post a strong pollen CADR and a weak smoke CADR, and pollen is the number brands prefer to advertise.
VOC Filter: the best air purifier for wildfire smoke should also have at least 1 pound of activated carbon, which works as a VOC filter that removes toxic gases. Wildfire smoke isn't just burning trees, it’s also burning homes, cars, wiring, insulation, and plastics, which produces formaldehyde, benzene, acrolein, and carbon monoxide. HEPA filters can’t capture gases. Only activated carbon, potassium, or zeolite can. Read more about how VOC filters work in the next section of this FAQ.
My recommendations are listed above, and here are some practical considerations:
Run the air purifier continuously, not just when you're in the room. Smoke keeps infiltrating through gaps even with everything shut.
Prioritize the bedroom since you spend the most time in it, and sleep is time for recovery.
Oversize on purpose. Rated coverage assumes an 8-foot ceiling and a sealed room, and a smoke is so small, it finds its way in easily.
Skip anything with an ozone generator or a non-defeatable ionizer. Ozone is a lung irritant, and adding it to smoke-stressed lungs makes things worse.
How VOC Filters Work
Gases, VOCs, and odors that pass through a VOC filter, AKA gas adsorbent, are caught, trapped, and affixed permanently to its surface.
A gram of activated carbon holds roughly 1,000 square meters of surface, folded into pores. A single pound works out to somewhere near 85 football fields of surface. This is why weight matters so much for how well a gas adsorbent works: fifteen pounds of carbon-zeolite has thirty times the surface of half a pound, so it holds thirty times as much before it fills.
What is adsorption vs absorption?
Adsorption describes something that happens on the surface; absorption describes something being fully permeated, like a sponge soaking up water.
What are VOCs?
VOCs are Volatile Organic Compounds. They volatilize, AKA are easily released from their sources into the air around them at room temperature. Here, "organic" refers to carbon-based chemicals, not organic in the sense of pesticide-free and healthy.
VOCs are gasses, and some, but not all, have an odor.
Are VOCs harmful?
Some VOCs, but not all, are harmful to health. Some of the well-studied harmful VOCs are:
Formaldehyde is the most well-known harmful VOC (it’s a carcinogen) and is found in furniture glues, new carpet, sealants, stains, and finishes on wood furniture or flooring, engineered wood and particleboard, paints, area rugs with synthetic backing and glues, and cleaning products.
Benzene is another VOC that’s a known human carcinogen: it causes leukemia, and the evidence behind it is strong. Indoors it comes from attached garages, tobacco smoke, fuel, and some paints and adhesives.
Toluene and styrene are also harmful. Toluene is a neurotoxicant found in paints, adhesives, and nail products. Styrene comes off polystyrene and some resins.
Not all are harmful: the scents plants release, essential oils, and food smells are all VOCs that are typically neutral or even good for our health.
Why are VOCs harmful?
VOCs can cause harm in two ways: by irritating your airways, and by passing through your lungs into your bloodstream, where they affect the rest of your body.
Airway irritation: This is the harm people expect. VOCs can contribute to asthma, allergy, and other lung issues, along with irritation of the eyes, nose, and throat.
Body wide: VOCs are gases. When you breathe in, they travel all the way down to the alveoli, the air sacs at the very end of your airways. This is where oxygen crosses the thin lung lining directly into your bloodstream. That lining is about two microns thick, and it is built to let small molecules through. It can’t tell the difference between oxygen and a VOC from a solvent. VOC molecules are very small, so they diffuse straight across. In rat studies, VOCs like trichloroethylene show up in arterial blood within a minute of the first breath. How much of any given VOC crosses over depends on the compound, but the pathway is short and fast. This is why VOCs can give you a headache: VOCs reach your head through your bloodstream.
Is the “new house smell” dangerous?
The "new house smell" is VOCs off-gassing into the air, and the smell itself is a poor guide to whether they are harmful. Most of what you smell is solvents and terpenes from fresh paint, finishes, furniture glues, and manufactured wood products. Those escape quickly and drop off quickly: total VOCs can fall 77% in the first 23 days.
Formaldehyde is different: it is one of the VOCs classified as a carcinogen, it decays far more slowly, and it is not always detectable by smell. In new homes, most VOCs fall to older-home levels within a year, while formaldehyde takes considerably longer. So a strong smell means ventilate, but no smell does not mean you are finished. Open windows are the fastest fix, and an air purifier with enough activated carbon helps when opening windows isn't an option.
Why do most air purifiers focus only on PM2.5 and not VOCs?
Purifiers focus on particles for three reasons:
First, particles are easily measurable and always harmful, whereas gases are hard to measure and a mixture of harmful and harmless. A basic sensor counts particles well enough to put a live number on a display, but most consumer VOC sensors are unreliable, expensive, and none can tell the difference between a harmful vs. harmless VOC. VOCs are not just one thing; they are thousands of compounds ranging from formaldehyde to the natural scent of pine wafting in from your backyard.
Second, the research on PM 2.5 is much stronger than it is for VOCs simply because PM 2.5 is a major outdoor air pollutant with decades of environmental research and funding behind it. There is a regulatory monitoring network for particles, so a study can estimate what hundreds of thousands of people breathed using nothing but their home address. Nothing like this exists for VOCs, partly because indoor measurements are difficult to research and especially because the complex mixtures of VOCs vary so much from home to home. Measuring them means putting instruments inside the house, one house at a time. So the gap between PM 2.5 and VOCs is about what is easy to study, not necessarily about what is safe, and the uncertainty is real. We do know a little: a systematic review of objectively measured indoor air found insufficient evidence that indoor PM2.5 affects adult asthma, and strong evidence that VOCs, especially aromatic compounds, are associated with increased asthma symptoms.
Third, there is no commonly used US standard for gas removal, so there is nothing to hold a company to. HEPA means something specific and testable: 99.97% of particles at 0.3 microns. CADR, the rating on the box, is measured with smoke, dust, and pollen, which are all particles. There is no CADR for VOCs, and "carbon filter" has no definition behind it at all, so the same two words describe fifteen pounds of carbon-zeolite blend and a sheet of mesh with carbon dust sprayed on it. This is why I rate gas removal by carbon (or other adsorbent mineral) by weight.
Most air purifier brands focus on what has the most research behind it, what is easily measured and tested for. As awareness of VOCs rises, especially with the odors and VOCs associated with wildfire smoke, more are turning toward increasing their VOC adsorbent capacity.
Which is more dangerous, PM 2.5 or VOCs?
PM 2.5 has much more research backing up how dangerous it is, and more is coming out all the time. It is increasingly linked with diseases related to inflammation like dementia, heart disease, and other chronic illness. When it is in your house, like during wildfire events, opening the windows in a polluted city, and during cooking, burning fires or candles, it is dangerous and should be removed.
Why is it important to remove VOCs?
It’s important to remove VOCs from your indoor air for three reasons:
VOC exposure is continuous. Particle exposure is episodic: PM2.5 in a home spikes when you cook dinner, when there is a wildfire that comes in through cracks in your house, or you light a candle. Between events, levels fall back down. VOCs on the other hand are continuously off-gassing from building materials, furniture, and decor: cabinetry, flooring adhesive, paint, foam, engineered wood, upholstery.
Several individual VOCs are established human carcinogens. Formaldehyde is classified by the International Agency for Research on Cancer as a Group 1 human carcinogen, causally linked to nasopharyngeal cancer and leukemia. Benzene is also Group 1, causing acute myeloid leukemia, and it gets indoors from attached garages, some paints and adhesives, and tobacco smoke. Toluene is a neurotoxicant.
Regulation doesn’t exist. Furniture, decor, paints, candle scents, and personal products generating VOCs indoors don’t have any regulation or limit, which means the only exposure control is what you choose to buy and what you choose to filter.
VOC research hasn’t caught up with particle research because indoor air and complicated combinations are very hard to study, not because they’re less of a problem.
Do air purifiers remove VOCs?
Yes, if it has activated charcoal, zeolite, or another gas adsorbent working as a VOC filter. Gasses are not particles, and therefore cannot be captured by a HEPA filter. An adsorbent is used instead. Adsorption is a chemistry-based process that works when a gas clings to the surface of the adsorbent, where it stays trapped. Activated charcoal is very good at capturing a wide range of odors (also called VOCs) from the air.
A simple carbon cloth will not capture much, but if a pound or more of activated carbon is added, that increases the ability to adsorb odors. Sometimes, mineral mixtures are added to activated charcoal to increase the types of VOCs that can be adsorbed from the air. Potassium iodide, potassium permanganate, and zeolite are three different mixtures that are commonly added because each has a different pore size that can adsorb different chemicals better than charcoal alone. Zeolite is capable of adsorbing formaldehyde, which is important, because charcoal cannot do it on its own.
I also recommend removing VOCs from the source— purchasing low-VOC furniture and decor, and not using scented products (or choosing safer ones).
Do air purifiers help with VOCs?
Yes, but only if it has VOC filtration media in addition to a HEPA filter. VOC filters are able to capture gases that are too small for HEPA filters. If you have a lot of new building or new furniture off-gassing or deal with cooking odors on a regular basis, opening a window for ventilation is useful, but VOC filters will help, too, especially when opening windows isn’t practical on hot days or days with outdoor air pollution.
Do air purifiers remove odors?
Yes, if they have a meaningful amount of gas adsorbent, air purifiers can remove odors. Odors are complex combinations of VOCs.
What is a VOC filter?
A VOC filter is one layer of an air purifier that can remove Volatile Organic Compounds (gases, odors) from indoor air. Depending on the model or brand or air purifier, a VOC filter is usually made of activated carbon, or a blend of carbon and other minerals that are capable of capturing gases in the tiny pores. VOC filters typically come in one of four different forms:
A carbon-composite HEPA Filter: this is a HEPA filter coated with a layer of activated carbon. The carbon is bonded directly onto the HEPA filter, so it appears black or very dark grey (HEPA filters are normally white). This combination can capture some VOCs, but because it’s just a thin layer, offers the least amount of VOC filtration.
Carbon pad: A cloth or sheet of foam impregnated with activated carbon. These are common in many air purifiers because they’re lightweight and inexpensive and are sometimes called a deodorization filter. These often have more carbon than a composite HEPA filter, but not as much as honeycomb style trays or canisters, so will not last as long or capture as many VOCs. An advantage of these is that the HEPA filter is not blocked and filtration efficiency stays really high.
Honeycomb style tray: these are rigid rectangular mesh filters that you place in front of a HEPA filter inside of an air purifier that removes VOCs. These are filled with activated carbon pellets, which have much more surface area than the carbon embedded in a cloth. Depending on the brand, these typically contain between 0.3-1.5 lbs of carbon pellets. HEPA filtration efficiency can stay very high with these, as well.
Canister: these are large cylinders filled with several pounds of carbon. Sometimes other VOC filter material is added, like potassium permanganate or zeolite, which can capture formaldehyde. These have the best VOC filtration abilities, but can slow the HEPA filtration speed down because moving air through it takes longer.
For most people, an air purifier with a honeycomb-style VOC filter strikes the best balance between VOC and HEPA particle filtration.
What is the best air purifier for VOCs?
The best air purifiers for VOCs, smells, odors, and harmful gasses contain substantial activated carbon on the order of pounds (not just a cloth). Carbon holds gas molecules on its surface, and when it fills, the filter stops working. Half a pound of carbon vs fifteen pounds makes a huge difference in how long they last.
Formaldehyde is the exception:. Formaldehyde is a small, highly volatile molecule, and plain carbon holds it poorly. It still helps, but mineral media does better: potassium permanganate oxidizes formaldehyde instead of only holding it, and amine-treated carbon works by similar chemistry.
If a new build or new furniture is your reason for buying, look for a blend to capture both formaldehyde and the general VOC mixture.
Air Flow
Air Flow through Air Purifiers
An air purifier with excellent filters won't work if it's not capable of moving air through it, if it does so very slowly, or if the air escapes around the edges of an unsealed filter.
The second component of what to look for in the best air purifier is its ability to circulate air through the filters at speed. Airflow determines how much of your room's air actually reaches that filter, and how often.
The problem is, the numbers can be really confusing and easily manipulated to seem better for you than they are. Understanding the difference between CFM, CADR, and ACH is a really helpful tool to prevent being misled by sneaky air purifier marketing.
What do CFM vs CADR vs ACH mean?
These measurements are about how much air flows through a purifier, how well that air is cleaned, and how long it takes that clean air to reach the whole volume of your room. CFM is the least useful number, CADR is helpful for comparing models side by side, and ACH is the most specific for your home.
CFM = Cubic Feet per Minute. Least useful. The CFM is how much air is pulled through a machine each minute. It says nothing about whether that air actually gets purified, and doesn’t consider the size of your room.
Calculation for your home: not very useful. You can look for at least 100 CFM for every 250 square feet of space, which works out to roughly 3 air changes per hour at standard 8-foot ceilings. But, this won’t tell you how well the air purifier actually works. Even if it has a true HEPA filter, it may not be sealed well. CADR is a much better indicator.
CADR = Clean Air Delivery Rate. Helpful. Cubic feet of clean air per minute an air purifier is capable of delivering. The CADR is the CFM multiplied by the efficiency of the filter. That means it captures both how much air moves and how much of the contaminants get removed from that air. CADR is tested in a lab in a sealed chamber, and brands will often show the results to prove their machines work well. The CADR is reported as three values: smoke, dust, and pollen (these are stand-ins for small, medium, and large particle sizes). A CADR tells you nothing about formaldehyde or other VOCs. But CADR is still useful because it catches bad purifiers that have an impressive-sounding CFM but a weak filter: in these, air moves through fast, but doesn't get clean, and the CADR comes out low.
Calculation for your home: look for an air purifier with a CADR two-thirds of your room's area. For example, a 20 x 15 foot room has an area of 300 square feet. So a CADR of 200 minimum would be ideal. (200/300 = 2/3). This rule assumes 8-foot ceilings. Note: CADR is reported in units of CFM, which you'll see on brand spec pages. That's correct, not a typo. Both are cubic feet per minute; CFM counts any air moved, but CADR’s CFM results count only the portion that came out clean.
ACH = Air Changes per Hour. How the machine’s CADR works for your specific room's total volume (square footage and ceiling height). This is something you have to calculate yourself; it’s not a property of the air purifier itself but how well it will work in your space, given how large a volume it is. It’s the most accurate way to predict how well a purifier will work in your space because it takes your ceiling height into account instead of assuming 8 feet.
Calculation for your home: ACH = (CADR × 60) ÷ (square footage × ceiling height). An air purifier with 4 to 5 ACH is ideal for regular use. Go to 5 or higher for allergies, asthma, or wildfire smoke season.
One important note: CFM and CADR (and therefore ACH) are calculated at max fan speed, which is often too loud and intense for a home. Choosing a model with numbers higher than you need may be best if you don’t plan to run your air purifier on its top speed all the time.
What does suggested room size mean for air purifiers?
Suggested room size is the square footage a brand says its purifier covers. It is not a standardized figure, which is the problem. Three separate assumptions go into it, and a brand can adjust any of them to make their purifier seem better than it really is. Some are honest, though! Here’s what to look out for:
How many air changes per hour: AHAM, the official highest standard, says 4.8 air changes per hour means an air purifier is doing a good job. Many brands use 4, some use 2, and some use 1 while still calling it "cleans."
Which CADR: smoke is hardest to catch, so the smoke CADR is the most telling. If a brand uses their smoke CADR, that’s the more impressive choice. Pollen is much easier to catch, so a pollen or averaged CADR is less impressive.
Ceiling height: brands assumes 8 feet for the volume of their suggested room size. If you have higher or vaulted ceilings, you have a bigger volume, and the air purifier won’t work for you as well as they state.
The same purifier can honestly be advertised at 525 sq ft or 2,520 sq ft depending on what details are used. Always check what air change rate a coverage claim assumes. If it isn't stated, assume it's an overstatement and use the CADR to calculate what will work in your space (ACH = (CADR × 60) ÷ (square footage × ceiling height). An air purifier with 4 to 5 ACH is ideal for regular use. Go to 5 or higher for allergies, asthma, or wildfire smoke season.)
What does AHAM Verifide matter for CADR numbers?
Because it’s the most rigorous version of CADR testing.
CADR is a test method, and any brand can hire a lab to run it and publish whatever comes out. That's better than nothing and many labs are being honest while saving on the high costs that AHAM Verifide certification might cost. But, what the AHAM Verifide certification adds is longer term accountability. The air purifier units get randomly selected and re-tested annually, results are published in their searchable public directory, and a tested unit has to stay within 90% of its certified smoke and dust values and 80% of pollen. If the air purifier falls out of compliance, it loses the certification.
Without certification, you get a CADR number from one unit the brand chose to show you. It may be real and lasting, but may be just from one moment in time. Like with any certification, the accountability that comes with third party testing is really useful. But, AHAM Verifide is voluntary and costs money, so even some very good air purifier brands skip it. The absence of AHAM Verifide numbers isn't proof that their machines don’t work, but just means the CADR depends on you trusting the brand's word.
For air purifiers without third party certification through AHAM for their CADR, just look for multiple independent testing outlets or labs data. Their numbers should all point toward the same level of performance and is a good second-best option.
What does AHAM Verifide Room Size mean?
AHAM Verifide Room Size = Smoke CADR x 1.5, assuming an 8 foot ceiling.
Some brands advertise a suggested room size instead of a CADR. The 1.5 in the equation above comes from the 2/3 rule solved backwards: if a CADR should be 2/3 of your room's area, then the area a given CADR supports is that CADR × 3/2, or 1.5.
This also means you can work in reverse! Divide an advertised room size by 1.5 and you've recovered the CADR the brand chose not to lead with.
AHAM's convention is to use the Smoke CADR, the hardest size of particle to capture. It's the conservative choice, and it's the one that makes the numbers comparable across brands.
If a brand uses the Pollen CADR instead, the easiest size of particle to capture, that inflates the room size by roughly 30% off the identical machine. The room it now recommends is one the unit can't actually keep up with for smoke or fine particles.
*Verifide is spelled correctly; it's not Verified, but Verifide. Why? I do not know, but I’m guessing it’s probably a trademark registration quirk.
The trade-off between VOC removal and particulate removal
Everything that removes pollution from air causes air to slow down as it goes through it.
An activated carbon bed is a physical obstacle: a deep layer of pellets has a lot of surface area for holding gases, and that density means the fan has to push harder to move air through it. The same is true of a very tight or heavily layered stack of HEPA filters. The same is true of medical grade H14 HEPA filters and ULPA filters. All of these cause pressure drop, which reduces the amount of air that gets processed per minute (CADR).
This is why some of the best VOC purifiers have less impressive CADRs and are less efficient at removing particles. The machine isn't poorly designed, but it's optimized for VOC, odor, and gas removal, rather than PM 2.5 removal. This is also why brands with really high grade HEPA filters, thick versions of HEPA filters, or a lot of carbon or mineral media, move air slowly. They will still clean air, but it will be slower. A bigger machine with a stronger motor can increase the chances it does both, but that often has the drawback of higher noise and energy use.
On the other hand, an air purifier with a thin carbon fabric can move far more air through faster, and clear smoke from a room quickly, but its VOC adsorbent capacity fills very quickly and it may not capture VOCs meaningfully at all.
This why I rate particle removal and VOC removal separately instead of blending them into one score, and why I consider noise levels.
Common misleading specs used by brands
CFM confused with CADR: some brands and air purifier review sites will mistake CFM (Cubic Feet per Minute) for CADR (Clean Air Delivery Rate). A high CFM doesn’t mean it’ll have a high CADR. CFM just measures how much air flows through a machine, not if any of it is getting clean. CADR is a much more useful number, because it measures how quickly air is cleaned. Importantly, and perhaps confusingly, CADR is measured in cubic feet per minute: just make sure you’re looking at a CADR’s CFM, not a regular CFM.
CADR in cubic meters per hour instead of instead of cubic feet per minute. A CADR with m³/hr looks a lot higher than a CADR measured in cubic feet per minute (CFM). Some brands will show the higher number, but the standard metric that most purifiers use, including AHAM third party testing, is cubic feet per minute.
CADR in disguise: “suggested room size.” This is essentially the same as CADR, and is sometimes used for helping customers, or sometimes used to hide a low CADR. Just Divide the advertised “suggested room size” by 1.5 and you get the actual CADR.
Pollen CADR instead of smoke CADR: If you see just one CADR published with no pollutant named, they might be using the pollen CADR. Pollen is easier to capture than smoke, so this number will be more impressive. If a brand shows one CADR instead of three, ask which one.
"Overall CADR." There's no such thing. CADR produces three values and they can’t be averaged because purifiers work differently on all three things. A single composite figure is either one of the three, or an average that hides the lowest one. If a brand shows one CADR instead of three, ask which one it is. They usually won’t tell you.
Air Change trick: "Cleans 2,520 sq ft in 1 hour" almost always means one air change, which removes about 63% of particles. The same machine held to the 4.8 changes per hour AHAM testing requires, would have a cleaning size 4.8 times smaller. Check to see how many air changes they’re talking about. I’ve seen brands use 1, 2, or the actual 4.8.
Inherited numbers: A brand tests one model and reuses the figure across a series. Air purifier re-designs can change CADR.
"True HEPA" as the only performance claim: It describes the filter, but not how well the air purifier pushes air through it. A HEPA filter in leaky housing lets air slip past it and that air won’t be cleaned.
What Good Quality Air Purifiers Remove
A good air purifier with all three filter layers (pre-filter, HEPA filter, and VOC filter) with good air flow is capable of capturing the following:
* Radon appears here only as its progeny, the solid decay products that deliver the dose. Radon gas itself is not captured by filtration, and it keeps producing progeny in the room, so source removal comes first. The two rows are the same element in two populations: fresh progeny form tiny unattached clusters, then stick to room aerosol to form the much larger attached fraction. HEPA removes the attached fraction well, which leaves proportionally more of the unattached fraction, and that one delivers more dose per unit. See my radon guide.
Bands mark which stage captures a pollutant first, not the only stage that can. A HEPA filter would capture pet hair too; the pre-filter simply reaches it first. The boundary between the HEPA and adsorbent bands is a matter of phase, not size: particles get filtered, gas molecules get adsorbed.
Common Air Purifier Gimmicks
What is a PECO air purifier?
PECO stands for PhotoElectroChemical Oxidation. It oxidizes micro-organisms, effectively killing them. This technology has been around for decades, but in 2016, was added to the Molekule air purifier. Unfortunately, it was found in multiple tests unable to filter out harmful particulate matter like PM 2.5 or other gasses nearly as effectively as regular HEPA filters can. The Molekule company was forced to retract these claims. While it is an interesting technology, with potential future applications, it remains just not as effective as regular HEPA filtration. The Molekule filter now has a HEPA filter and a PECO filter. This is a major and well-publicized version of healthwashing.
Are PCO air purifiers safe?
No. PCO stands for photocatalytic oxidation, and generates toxic byproducts including formaldehyde, acetaldehyde, benzene, and other harmful VOCs. The idea is nice: removing VOCs from air and using catalysis to break them down sounds good in theory. However, machines you can buy can’t do it well yet. More research is showing that they take VOCs from the air and transform them into more harmful VOCs. Use carbon or mineral blends to capture VOCs instead, and change the filter on schedule. This is a much more effective way to remove VOCs from the air safely.
What is UVGI?
UVGI stands for Ultraviolet Germicidal Irradiation. This technology does have the ability to kill microbes, however, in most home air purifiers, the air flows by it too quickly, leaving inadequate contact time for it to be effective. UVGI also does not address the main issues in most homes, which are particulate matter and VOCs, rather than microbes.
Additionally, UVGI can generate formaldehyde from incompletely breaking down VOCs.
What are air purifier ionizers?
Ionizers are an add-on to air purifiers that emit charged negative ions into the room. The ions attach to airborne particles like dust, allergens, and smoke, giving them an electric charge.
How effective are ionizers at cleaning the air?
They clean the air, but not the room. The particles that ionizers add a charge to are drawn to nearby surfaces like walls, furniture, floors, and even your own skin and lungs, settling out of the air. So while it’s true that it reduces particles in the air, and looks like effective air cleaning on a particle counter, it isn't gone: it's just been relocated onto surfaces around you, where it can get kicked back into the air (or into your airway) the next time something disturbs it.
Are ionizers safe?
Maybe. There’s only a little research on these, and the benefits and risks seem mixed at this point.
If an ionizer is strong enough to charge particles effectively, it's also very likely generating ozone, which is toxic to your lungs and causes inflammation.
The ion exposure itself also carries its own risk: a 2021 study had college students sleep with real vs. sham ionizers for a week each and tracked a biomarker of oxidative stress in their urine. The real ionizers did lower PM2.5 in the room, but ion exposure alone drove that stress marker right back up, so the net cardiorespiratory benefit came out to roughly zero. A 2019 study also showed that ionizers impacted students heart rate variability. Both studies were small, and there isn’t a lot of other evidence outside of them yet.
The only safety standard that exists for ionizers is CARB certification, which limits ozone output to 0.050 ppm. But it says nothing about the oxidative stress the ions can cause independent of ozone. There's no standard or certification that tests for this. While I consider ionizers more of a gimmick than a definite health risk, this is why I generally recommend just keeping the ionizer off and letting the HEPA filter take care of particles.
Why are air purifiers with ozone generation unsafe?
Ozone, O3, is the free radical version of oxygen. It is highly reactive with particles in the air, and also highly reactive with cells in your body. Breathing in ozone can cause lung inflammation and respiratory issues.
Air Purifier Alternatives
Best Air Purifying Plants: Do They Actually Clean Indoor Air? What plants clean indoor air best?
680 of any plant you like! The 1989 NASA study that’s often referenced as proof that plants can purify the air is wildly overstated. While it’s true that plants can remove some VOCs and carbon dioxide, this study only applies to a small, sealed, space station style environment. In a regular house, you would need about 680 plants to replicate those results. See my short video about it here.
Are probiotic air purifiers worth it?
No. While I love the idea of probiotics incorporated into homes, this is not an effective way to remove fine particulate matter (PM 2.5) or VOCs, which can have serious consequences for cardiovascular, lung, and cognitive health, from your air. Until I see third party testing showing one of these can truly remove PM 2.5, I consider these a form of healthwashing, or wishful thinking.
Are moss air purifiers worth it?
No, unless you had the equivalent of 680 house plants worth of moss. The 1989 NASA study that’s often referenced as proof that plants can purify the air is wildly overstated. While it’s true that plants can remove some VOCs and carbon dioxide, this study only applies to a small, sealed, space station style environment. In a regular house, you would need about 680 plants to replicate those results. See my short video about it here.
Until I see third party testing of PM 2.5 reduction by moss, I consider moss purifiers a form of healthwashing. They may be pretty, and certainly aren’t doing harm, but aren’t protecting you from dangerous particles, either.
Are water air purifiers worth it?
No. These are a gimmick. Until I see third party testing showing that PM 2.5 can be captured effectively by water, I consider these a form of healthwashing. They aren’t protecting you from dangerous particles.
Air Purifiers for Mold, Radon, CO2 & Dust: What Works and What Doesn’t
Do air purifiers remove radon?
No, HEPA filters cannot remove radon gas directly, with two exceptions. But first: take care of the source. Radon gas comes from uranium decaying in the soil and rock under your foundation, and it gets trapped in your house. The only way to truly fix it is professional remediation. Radon is the second leading cause of lung cancer overall and the leading cause among people who have never smoked.
One semi-exception: radon gas itself does little damage on its way through you. Most of what you inhale gets exhaled before it decays. The danger is what it decays into: smaller, solid, radioactive metals. These are called radon progeny, or radon daughters: polonium-218, lead-214, bismuth-214, and polonium-214. They come out of the decay electrically charged, so they stick to whatever they touch, including particles already floating in your air. That means the PM2.5 a HEPA filter is very good at capturing can have radioactive metals hitching a ride on it. However, when a purifier strips the particles out of your air, the progeny have nothing left to attach to. The "unattached" fraction goes up, and unattached progeny deposit in your lungs far more efficiently than attached ones do. One field study in a high-radon home found the purifier cut total progeny by 33% while the unattached fraction rose 174%. Most of the research still finds a net reduction in dose, but it's smaller than the particle numbers suggest, and the EPA has never endorsed air cleaners as a radon strategy. Treat this as a small side benefit of a filter you're already running, not a reason to run one.
The second exception: activated carbon does adsorb radon gas. This is the whole basis of the charcoal used in radon test kits. VOC adsorbent containing zeolite might capture a very tiny bit of radon, too. But a carbon or zeolite bed against a continuous radon source from the ground doesn’t last long. Progeny also settle into your dust and onto your furniture, where no air purifier reaches them.
Read my guide to radon testing and recommended radon detectors here.
Do any air purifiers remove CO2?
Unfortunately, no air purifier can remove carbon dioxide (CO2) from your home. It would take dozens of pounds per person per day of a mineral complex like zeolite to capture the CO2 just one person exhales. It would also require an extremely loud, heavy duty fan to push enough air through to effectively filter the CO2.
Why it would be helpful: It would be ideal if an air purifier could capture CO2 because we breathe it out all day long, and high levels in indoor air can cause headaches, lack of focus, and trouble breathing. Overnight, high levels easily build up in bedrooms with closed doors and windows, and can lower sleep quality, affecting your cognitive performance the next day.
CO2 capturing tech used in space and under the sea: In submarines and on spaceships, they prevent CO2 buildup using the mineral mixture method (like zeolite or lithium hydroxide). Large, heavy canisters are used each day to capture CO2, then stowed away. Though your home is not a space ship, during a wildfire, when you’re sealing up the house and running air purifiers, you may be able to capture VOC and PM 2.5 well, but CO2 levels will likely continue to climb.
Plants: Plants can break down CO2 through photosynthesis, but you would need several hundred in each room of your house to effectively remove any CO2.
Future Research: Research is underway to figure out how we can capture more of the CO2 on earth, possibly helping to cool our environment.
Practical advice for now: For now, your best bet is to open windows for ventilation when outdoor air quality is good, or use an HVAC system that pulls fresh air into your house. When fresh air isn’t reasonable due to wildfires or other outdoor pollution, minimize CO2 levels as much as possible: refrain from heavy exercise and cooking (which also generates CO2) indoors.
Can air purifiers remove carbon monoxide?
No. CO is a gas molecule that neither HEPA filters nor VOC filtration media like activated carbon can capture.
There are catalysts that convert CO (hopcalite), but they’re in industrial respirators and mine rescue gear, not air purifiers for your house.
This matters because carbon monoxide is lethal, odorless, and colorless, and an air purifier will not protect you.
Practical advice: use a CO alarm on every level of your home. Have all of your fuel-burning appliances (furnace, water heater, gas stove, fireplace) checked every year. Run your range hood exhaust fan, vented outdoors whenever you cook, and never run an engine or generator in an attached garage. If the CO alarm sounds, get outside and call 911.
Can an air purifier help with mold?
Yes, air purifiers can help with mold in two ways:
First, it can capture mold spores, fungal fragments, and the mycotoxins that are catching a ride on particles that are floating freely in the air. This reduces the chances they will land and overgrow on a humid or damp area. Any air purifier with a HEPA filter and a high CADRs (Clean Air Delivery Rates) will be able to capture these. You don’t need special technology for this, and some tech marketed toward mold is not just unnecessary but harmful (like UVGI or PCO), adding ozone or formaldehyde into the air.
Second, an air purifier with activated carbon or mineral VOC adsorbent can adsorb mold-associated VOCs and odors from the air, making it smell less musty.
Use a dehumidifier to prevent excess humidity and dampness in conjunction with using an air purifier for mold.
Removing the source of mold is the most important step. Hire a mold inspector and consider remediation. See my list of resources here.
Do I still need to dust with an air purifier?
Yes, but less often. Air purifiers are very efficient at capturing airborne dust, but are not strong enough to lift dust that settles on surfaces in your room off into the air.
Best Air Purifiers for Allergies: Do They Help with Symptoms?
Can air purifier help with allergies?
Yes, an air purifier can help with allergies in three ways.
First, it can trap large particles like pollen and pet hair on its pre-filter.
Second, an air purifier with a HEPA filter is great at capturing smaller particles like mold spores, dust mite debris, and even cooking or wildfire smoke particles that can irritate the lungs, nose, and throat.
Third, an air purifier with activated carbon or minerals can remove irritating VOCs from the air, which also contribute to allergy and asthma even more than PM 2.5 does.
Air Purifier Placement Guide: How Many Do You Need Per Room?
Where should air purifiers be placed?
Prioritize placing an air purifier in your bedroom, where you spend 1/3 of your life. Sleep is also when your body goes about repairing cells and healing, so having clean air and a healthy environment is important to support this process. If you can consider two air purifiers, placing one between the kitchen and living area is ideal because it will help capture cooking particles and odors and make the air in your living area, where you likely spend the second-most amount of time, safe.
How many air purifiers do I need?
I recommend considering both the square footage the air purifier is certified to clean, as well as the unique shape of your floor plan and home’s air flow. There’s a bit of an art to it. For example:
If you have an open floor plan, choosing an air purifier can be as straightforward as checking the CADR with your room’s dimensions (see above.) Air purifiers generally don’t have to work as hard to replace the air and get around walls or through door openings in this case.
If you have a house with lots of separation between rooms, you can still get one air purifier with a large square footage rating, but it won’t work as well. If budget is a concern, and you can only afford 1 air purifier, consider helping the air move between spaces a little better by using ceiling fans or other quiet fans to encourage air movement. If that’s not possible, you might consider two smaller air purifiers to focus on better on cleaning the air in each room separately.
If you’re not sure, I recommend using an air quality monitor placed in the room or area farthest away from your purifier to see if it’s purification reach is adequate for you. Relying on a purifier’s built-in air quality sensor isn’t useful in this situation, since it’s only sensing the air immediately around it. I have several highly accurate air quality monitors listed here.
How often do I need to change air purifier filters?
It will depend on the size and type of filter you have, and if you go through any poor air quality events like a wildfire or other thick smoke. Every air purifier brand and model will tell you how often the filter needs to be changed based on regular use, and will often have an indicator light go off. However, I recommend always replacing the HEPA and carbon filters after smoke events like wildfires.
How often do I need to turn my air purifier on?
Air purifiers are meant to be run 24/7 on their low setting, unless during times of high air pollution (wildfire, burning food indoors, or acute off-gassing from new furniture, for example.) If you want to save energy, turn air purifiers on whenever you get home, and start the one in your bedroom 20 minutes before you go to sleep so it has a chance to thoroughly clean the air.
How quiet should an air purifier be?
Anything under 50 decibels (dB) is typically quiet enough for bedroom use. For reference, 50dB is about the sound you’d hear in a quiet office, or coming from a quiet refrigerator. It’s generally considered a reasonable and safely quiet level for sleep, though of course your sensitivity may vary.
When sound is unwanted, and affects the health and well-being of people or other living creatures, it meets the definition of noise pollution. The EPA confirms that it’s not just an annoyance, but is as important to your health as other types of pollution are, like air or water pollution. Excess noise, especially at night, can actually contribute to heart attack, and have negative impacts on cardiovascular health, including high blood pressure.
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