A great air purifier can really improve your life. But to qualify as great, it needs to be powerful enough to clean the air in a large living room or playroom, quiet and dark enough for you to sleep near it in a bedroom, and inexpensive enough that it’s reasonable to have several spread throughout your home. Few machines meet that standard, but after seven years of testing 35 different air purifiers, we believe the exceptional Coway AP-1512HH Mighty is the best among them—as we have since 2015.
Within 30 minutes, the Coway AP-1512HH Mighty reduced heavy smoke pollution in a 135-square-foot, 1,215-cubic-foot New York office by as much as 98.9%. In past tests, it performed equally well in a 200-square-foot, 1,600-cubic-foot New York City bedroom. And when we tested it during ongoing smoke conditions in a vast Los Angeles conference room of nearly 10,000 cubic feet—more than twice as large as the Coway Mighty’s specs would seemingly allow—it cut particulate pollution by almost 70% in an hour. It’s a great value, at an up-front price often under $200 (and about $470 over five years, factoring in electricity and replacement filters). The Mighty’s compact form, quiet operation, and ability to shut off its display lights make it especially well suited to bedrooms. In long-term use, we’ve repeatedly confirmed it works like new even with filters used continuously for a year or more.
The Coway Airmega 200M is made by the same company as the AP-1512HH Mighty and is virtually identical to that model in every important respect, namely the controls, noise, and performance. Their filters and even their faceplates are interchangeable. And like the Mighty, the Airmega 200M has a display-shutoff feature that lets you dim its lights, something we value highly for bedroom use. The Airmega 200M has a square grille rather than a round one—but that’s the only major physical difference. If you prefer the Airmega 200M’s looks or if you find it at a better price, we recommend it just as highly.
The Blueair Blue Pure 211+ is our choice among air purifiers for large spaces of up to 650 square feet, especially spaces with open floor plans or high ceilings. With the ability to filter more air per hour than our top pick, the Coway Mighty, it works faster to achieve and maintain low particulate levels in such challenging rooms. The up-front price and running costs of the Blue Pure 211+ are much higher than those of the Coway Mighty (totaling about $1,150 over five years), but that’s comparable to most other large-space purifiers we’ve looked at. It was an exceptional performer in our testing, and it’s quiet and attractive to boot. All that said, unless you really need to clean a particularly large space, the quieter, smaller, and more affordable Coway Mighty is usually a better option.
If you need to clean the air in a space of around 200 square feet, the Levoit Core 300 is a solid and inexpensive purifier. It was impressive in our tests, reducing particulates by more than 97% on its high setting in 30 minutes in a 135-square-foot New York City office. On medium, it reduced them by more than 92%. It’s attractive and compact, measuring just 14½ inches tall and 8½ inches in diameter, and its display-shutoff feature means it won’t interrupt sleep with bright lights. At around $100 to purchase, it’s also the cheapest up front of all our picks. But it’s not terribly energy efficient: Running it 24/7 on medium will consume about $300 of electricity over five years, and seven new filters in that period will cost $180, making it slightly more expensive than the Coway Mighty long term. And it doesn’t keep pace with the Coway or the Blue Pure 211+ in larger rooms.
This model’s HEPA filter removes particulates (like pollen and smoke) from the air, and its second filter efficiently removes odors and VOC gases—an ability many purifiers lack.
If your environment has high levels of both particulates and volatile organic compounds (VOCs, or more broadly, odors), we recommend the Austin Air HealthMate HM400. Its massive 15-pound VOC filter bested all others we tested by a wide margin, and its HEPA filter offered excellent performance on particulates. The HealthMate’s performance comes at a price, however: Costing about $500 to $600 up front and averaging around $1,200 for five years of use, it’s the most expensive machine we recommend. You could buy and run three Coway AP-1512HH Mighty purifiers for about the same cost, and if particulates are your main concern, doing that instead will let you remove particulates from more rooms and a larger overall area.
Everything we recommend
This model’s HEPA filter removes particulates (like pollen and smoke) from the air, and its second filter efficiently removes odors and VOC gases—an ability many purifiers lack.
- Why you should trust us
- What can an air purifier do for you?
- Can HEPA air purifiers capture the coronavirus?
- Can air purifiers help with wildfire smoke?
- How we picked
- How we tested
- Our pick: Coway AP-1512HH Mighty
- Runner-up: Coway Airmega 200M
- Upgrade pick: Blueair Blue Pure 211+
- Budget pick: Levoit Core 300
- Also great: Austin Air HealthMate HM400
- What if you just put a furnace filter on a box fan?
- What settings should you run an air purifier on?
- How HEPA filters work
- Molekule Air and Air Mini: The worst air purifiers we’ve ever tested
- The competition
- How to set up, use, and maintain your air purifier
- What to look forward to
- Frequently asked questions
Why you should trust us
Tim Heffernan has been at Wirecutter since 2015 and has overseen this guide since then. Since 2017, he has conducted extensive real-world testing of air purifiers in his New York City apartment and in Wirecutter’s New York and Los Angeles offices. Tim has also lived with most of our picks, running them 24/7 for months—sometimes years—on end in his apartment. That experience has helped him gather objective data on their long-term purifying performance and any mechanical degradation. It has also helped him make informed judgments on factors such as ease of maintenance and operation, the presence or lack of distracting noises or lights, and simple visual impact—the so-called little things that, if done wrong, can make what should be a nearly set-it-and-forget-it appliance into a daily annoyance.
John Holecek, who co-wrote and performed testing for previous versions of this guide, holds a master’s degree in earth science, with a focus on climate, aerosols, and analytical chemistry. He has conducted laboratory tests for Wirecutter’s air purifier reviews since 2014. Since 1999, he has studied particulate air pollution for the National Oceanic and Atmospheric Administration and in the private sector.
What can an air purifier do for you?
HEPA air purifiers do one thing and do it very well: remove fine particles from the air. They are especially good at rapidly filtering out the most common airborne allergens, including dust and pollen; mold, mildew, and fungal spores; pet dander; dust mites and their excrement; soot from automobiles; and tobacco, marijuana, and wildfire smoke. HEPA purifiers also capture many airborne pathogens, including most bacteria and viruses. For a detailed discussion of their potential impact on the COVID-19 coronavirus, see the following section.
Air purifier owners offer extensive, almost universal testimony that the machines improve their sleep, reduce their allergies, or lessen their asthma symptoms, and recent studies have begun investigating an association between particulate pollution and degenerative brain disorders, including Alzheimer’s disease and Parkinson’s disease. Air pollution from US combustion emissions alone results in 200,000 premature deaths a year, according to a 2013 MIT study.
However, in the US air purifiers cannot be marketed as medical devices. That’s because it is exceptionally difficult to disentangle the known air-quality impacts listed above from other environmental and genetic factors that influence health.
HEPA (high-efficiency particulate air) filters don’t capture volatile organic compounds (VOCs, or more broadly, odors and fumes). To reduce them you need significant amounts of an adsorbent (typically activated carbon and/or alumina, which chemically bind to and neutralize the VOCs). Some also employ a class of minerals known as zeolites, whose extremely fine pores allow them to function as molecular filters. Our VOC pick has significant amounts of both activated carbon and zeolites.
No air purifier can do anything about allergens, bacteria, or viruses that have settled on furniture and other surfaces. To remove allergens like pet hair and pollen, you’ll need a vacuum cleaner or dust mop. To get rid of viruses and bacteria, you’ll need a disinfectant cleaner.
Can air purifiers help with wildfire smoke?
Yes. HEPA air purifiers are extremely efficient at removing smoke particles from the air. (We use smoke to test them, in fact, so our picks directly reflect their ability to remove it.) But in a wildfire event, purifiers are part of a larger smoke-mitigation strategy. It’s helpful to think of them as a central piece of a comprehensive plan that we detail in a separate guide, The Best Wildfire Preparedness Supplies and Strategies.
How we picked
We split air purifiers into three distinct “sizes”: those designed for small spaces like kids bedrooms, dorm rooms, and offices; those for general living spaces such as enclosed living rooms and master bedrooms; and those for large spaces like combined living/cooking/dining spaces or spaces with cathedral ceilings. The categories also broadly correspond to price—the larger the space, generally the more expensive the purifier you need to keep the air clean. As a rule, it’s wise to “oversize,” which will let you run your purifier on slower and quieter settings while still cleaning a room’s air effectively.
To sort purifiers into these three categories, we calculate their air changes per hour, or ACH, in hypothetical rooms of 150, 350, and 500 square feet (we assume 8-foot ceilings). This unit of measure represents how many times a purifier can circulate the volume of air in a given room in 60 minutes, and it provides a standardized baseline for categorizing and initially comparing purifiers. We set 4 ACH as the minimum for a given purifier to be considered adequate for each room size. Based on our seven years of testing, we know that 4 ACH ensures rapid and nearly complete cleaning of highly polluted air—a big concern during, say, a wildfire—and that anything below 4 ACH typically results in measurably worse performance.
Using ACH to categorize air purifiers overcomes a common problem in the way manufacturers rate their air purifiers in their advertising. Most offer a square-footage rating because it’s easy for a prospective customer to take their room’s dimensions and pick a purifier accordingly. But square-footage ratings are essentially meaningless when you’re comparing two rooms with different ceiling heights. Manufacturers also calculate their ratings in different ways, often resulting in inflated square-footage claims. Using ACH, which measures volume, gives us a true picture of a machine’s capability.
It’s important to note that our 4 ACH calculation is based on the maximum volume of air that a purifier can move on its highest setting. You’d use that setting in an extreme and ongoing pollution situation, such as when you’re dealing with a nearby wildfire. But on their highest setting, most purifiers are too loud—above 50 decibels—to be tolerable as a background for conversation, sleep, or TV watching. So we always oversize our picks, confirming that they can keep the air clean on their medium, “quiet” setting in a room of the recommended size.
Generally we only test purifiers with HEPA certification. In the North American definition, “true HEPA” means that a filter removes at least 99.97% of airborne particles of a 0.3-micron diameter in a single pass. (Human hair, for reference, is usually between 20 to 180 microns across.) That 0.3-micron diameter is not arbitrary: It is considered by the Association of Home Appliance Manufacturers, a trade group, the toughest size of particle to remove by physical, HEPA-type filtration. We go into detail on the physics of the process in How HEPA filters work below.
Among our picks, there is one exception to this general rule: the Blue Pure 211+, our pick for large spaces. It is not true-HEPA rated, but is certified by AHAM to have a clean air delivery rate of 350, and performed exceptionally well in our testing, where we measure each purifier’s effectiveness at capturing HEPA-standard 0.3-micron particles. CADR numbers in effect give the cubic feet per minute of perfectly pure air that a purifier can produce on its maximum setting. The CADR tests measure purifier effectiveness on three different pollutants—tobacco smoke, dust, and pollen—that correspond to particles of 0.09 to 1.0 micron, 0.5 to 3.0 micron, and 5.0 to 11.0 micron, respectively, so in a sense they are a tougher standard. (The HEPA 0.3-micron standard falls within the scale measured by the tobacco-smoke test.)
In addition to these objective measures, we weigh the value each purifier offers, without setting a strict price limit within each room-size category. To judge value, we compare specs (especially ACH), our test results, the findings of other independent reviews, ratings from owners, and manufacturers’ histories of reliability and customer service. This step lets us eliminate the many purifiers that cost far more up front than their specs and ratings justify. We also calculate the long-term ownership costs of our finalists by factoring in the cost of fresh filters and electricity consumption over five years.
We do not prioritize smart functionality, which generally means receiving more information from and having more control of a purifier via an app. We don’t consider smart functionality a necessity because our years of testing have proven that a good air purifier will create and maintain excellent air quality simply when allowed to run continuously on a moderate setting. However, we can see the appeal of having more information. We’ve published a separate guide to air quality monitors, which we’ve found are often the best way to get a greater understanding of a purifier’s effects on your air quality, even though they’re standalone devices that don’t directly control the purifier’s operation.
We do not dismiss purifiers that have ionizers in addition to HEPA filters, but we don’t look for this feature. Ionizers impart a negative electrical charge to air molecules that pass through the machine. These ionized air molecules then in theory bind to airborne particles and give them a charge, encouraging them to stick together and create larger particles that may be easier to filter or large enough to settle out of the air. The feature’s efficacy is uncertain (although it definitely increases the machine’s power consumption). Most purifiers with an ionizer let you toggle the feature on or off.
We do dismiss air purifiers that rely on ozone (O3, a molecule composed of three oxygen atoms) to “purify” the air. The theory is that ozone, which is highly reactive, neutralizes or breaks down pollutants. Setting aside the dubiousness of that claim, even low levels of ozone can be harmful (PDF). It’s crazy to introduce a new pollutant when the goal is to reduce pollution overall. Ionizers produce a small amount of ozone as a by-product, but as laid out by the strict California Air Resources Board, none of our picks with an ionizing function exceed the 0.050-parts-per-million (50 parts per billion) limit.
In 2019 the above criteria left us with 13 purifiers to test: four of our existing picks and nine new contenders. Our 2020 testing was disrupted by the coronavirus outbreak, but we tested three additional models early in the year. This increased the total number of air purifiers we have tested since 2014 to 35—on top of the dozens of competitors we’ve evaluated and dismissed without testing over the years.
How we tested
We’ve been testing air purifiers since 2013, and we have always judged them not just by how well they perform but also by how easily you’ll be able to live with them running constantly in your bedroom, living room, or office. We measure livability factors such as how much noise they make when running, as well as their long-term costs for energy consumption and replacement filters. And we consider subjective factors like the ease of operation and maintenance, the presence or absence of distracting lights (which can disrupt sleep), the user interface, and the physical size and aesthetics.
But air-purifying performance is paramount.
Over the past seven years, we have conducted both lab-based and real-world tests of air purifier performance. John Holecek conducted the lab tests in his San Diego facility, with professional-grade equipment used for atmospheric research (specifically a TSI 3080/3010 Scanning Mobility Particle Sizer and 3321 Aerodynamic Particle Sizer). Since 2017, Tim Heffernan has conducted multiple real-world tests in New York and Los Angeles, measuring particle concentrations with a TSI AeroTrak 9306, a handheld particle counter commonly used to certify air quality to OSHA standards in factories and other workplaces. All of the equipment measures particles down to the 0.3-micron HEPA standard; John’s equipment goes much finer, down to 0.01 micron, one-thirtieth of the size of the HEPA standard.
For the current guide, Tim tested the air purifiers in Wirecutter’s New York headquarters. In prior testing, he used his New York apartment and Wirecutter’s Los Angeles office.
2019 and 2020 New York tests
In 2019, Tim tested 13 purifiers over the course of two weeks in a 135-square-foot office with 9-foot ceilings (1,215 cubic feet, equivalent to our “bedroom” category) in Wirecutter’s New York office. In early 2020, he tested three more in the same space. He did not attempt to hermetically seal the room—after all, we wanted to see how the machines performed in real-world conditions—but he did take steps to make it more like a room in a typical home, sealing off the office’s powerful, filtered commercial HVAC ventilation with tape and foil to minimize its impact on air movement.
Tim conducted at least one pair of tests on each purifier: 30 minutes with the machine on its highest sub-50-decibel setting (about the upper limit of what we can consider comfortable for conversation), and 30 minutes with the machine on its absolute highest setting regardless of noise output. At the start of each test, he measured the ambient air quality for three minutes to get a baseline; after that, he burned five wooden matches and let the smoke circulate for two minutes to artificially raise the particulate levels in the air, and then he ran the machines for the remaining 30 minutes. Matches produce millions of very fine particulates, including those in the 0.3-micron range—the hardest size of particle to remove with mechanical filtration like HEPA.
Tim placed an AeroTrak 9306 particle counter 7 feet diagonally away from the purifiers, about 20 inches from both walls in the farthest corner of the room. This put the particle counter well outside the airflow path from the purifiers, eliminating the possibility of an artificially high measure of their performance and ensuring that the readings gave an accurate impression of the purifiers’ whole-room purification. The purifiers themselves sat at the midpoint of the long wall of the room, 2 feet from the wall, with no obstacles near their air intakes and outlets. The particle counter took readings continuously, with counts totaled in one-minute increments.
When retesting our existing air-purifier picks, Tim took four measurements, two using the old filters and two using new filters. Each machine had been running continuously on “quiet”/medium for at least six months in Tim’s apartment over the previous year, ensuring that the old filters saw heavy use. For the Molekule purifier, which uses a unique, non-HEPA method to remove particulates from the air, he took two measurements on each of the machine’s four settings (Silent, Auto, and Boost, corresponding to low, medium, and high fan speeds, and Dark plus Auto, in which the main purification method is off but the physical prefilter is in use). For the Dyson machines, which you can set to 10 different fan speeds—versus three, the amount for most purifiers—he measured on speed 10 (high) and speed 6 (corresponding to the medium-speed “quiet” setting on most other purifiers).
As we have for years, we normalized the data so that each machine’s peak represented the maximum particulate load it faced, specified as “100%,” and its overall performance represented its greatest reduction of particulates relative to that load. We believe this approach supports the best apples-to-apples comparison because it eliminates absolute particle concentration—which even under pure lab conditions is virtually impossible to exactly reproduce test-to-test and machine-to-machine—as the starting point in favor of a common measure. It isn’t a perfect approach, but given the multiple variables involved, it is the most accurate way to compare different purifiers.
In addition to these performance assessments, Tim measured the purifiers’ noise output at a distance of 6 feet, 3 feet from the ground, to determine their highest “quiet” setting (maximum 50 decibels, measured as dBA). He also measured their power draw on their lowest, medium, and highest settings, using the medium setting to calculate annual power costs.
In 2018, Tim conducted testing in his New York apartment similar to what he did in 2019 in Wirecutter’s New York headquarters. In his 200-square-foot back room, he ran 35-minute tests on each contender, on both “quiet” and high, and on (where applicable) both new and used filters, burning five matches to create a mass of fine particles and placing the AeroTrak particle counter far from the purifiers to measure their effects on the whole room.
In his 600-square-foot open-plan living/dining/kitchen space, Tim tested just the large-space contenders. The tests lasted for 65 minutes, the first five minutes to get a baseline reading of the ambient air conditions, followed by the burning of five matches and a full hour of measurements with the purifiers on. As always, Tim ran each purifier twice, once on high and once on “quiet.”
To test our advice to run your purifier on high for an hour to create very clean air and thereafter on “quiet”/medium to maintain it, Tim ran a three-hour test in the 200-square-foot room, using the top-pick Coway AP-1512HH Mighty and our large-space pick at the time, the Coway Airmega 400. At the outset, he burned 15 matches to create extremely elevated particulate levels in the room, as though a fire were burning nearby. He then ran the machines on high for an hour, turned them to their “quiet”/medium setting, and ran them for an additional two hours, with the purifiers and particle counter in their usual spots. We describe the results in What settings should you run an air purifier on?
He also tested a popular “hack”: taping a furnace filter to a box fan to create a DIY air purifier. He did a 35-minute, five-match test in the 200-square-foot room with a 20-inch-square Lasko box fan and a 20-by-20-inch Honeywell FPR 9 (roughly MERV 12) filter, one of our picks in our guide to furnace filters.
In 2018, Tim also tested purifiers in Wirecutter’s Los Angeles office, attempting to simulate wildfire conditions. He conducted these tests in a roughly 700-square-foot room with 14-foot ceilings, a space with a total of nearly 10,000 cubic feet—more than twice the volume of the 600-square-foot, 8-foot-ceiling New York test space, and bigger than what the large-space purifiers he tested were rated for. As such, it posed a stiff test for all of the machines.
Tim used slow-burning incense to simulate an ongoing wildfire smoke condition. (See our blog post about purifiers and wildfire smoke for more.) The tests ran for 65 minutes, with the machines on high. Tim placed the machines at the midpoint of the room, approximately 3 feet from the wall and away from any obstacles. He burned the incense near one corner of the room and put the AeroTrak particle counter between the purifier and the incense, roughly 12 feet from each. He let the incense burn (five sticks per test; sandalwood scent, if you’re wondering) for 15 minutes at the start of each test, getting a baseline reading of the room before the smoke had time to spread, and then measuring as the smoke/particle levels rose. After 15 minutes he turned each purifier on, set to high. The incense continued to burn for another 20 minutes or so, and the purifiers ran for 50 minutes total. This process resulted in: 1) heavy initial smoke conditions for the purifiers to deal with, 2) roughly 20 minutes of the purifiers dealing with both initial and ongoing smoke, and 3) roughly 30 minutes of the purifiers working to clear the air after the source of smoke had disappeared.
Our pick: Coway AP-1512HH Mighty
After a fifth round of testing, encompassing 32 different air purifiers and more than 400 hours of lab and real-world trials, the Coway AP-1512HH Mighty remains our pick as the best air purifier for most people. It has kept its place for so long for many reasons. In raw performance, it stands among the best purifiers we’ve ever tested, achieving as much as 98.9% removal of airborne particulates in just 30 minutes in our latest test. And it has maintained its high performance for years—we’ve tested the same machine three times starting in 2017, and it has always delivered similar results. The Coway Mighty is also unusually easy to live with, as it’s quiet and compact, and its display can go dark at night, making it a good fit for master bedrooms, playrooms, and living rooms or dens. Finally, it’s easily the most affordable purifier of its capabilities we’ve ever found: Adding up the purchase price, the costs of 24/7 operation on medium, and the costs of annual filter changes, you’re looking at about $470 over five years (or less: we calculate electricity costs at New York’s rates, which are 50% above the national average).
On the high setting in our 2019 New York City real-world test, the Coway Mighty reduced 0.3-micron particulate levels by 98.9% in 30 minutes, on both new filters and those that the machine had run on continuously for a year. On the medium setting, it reduced the 0.3-micron particulates by a statistically identical 87.7% and 87.6%, on new and old filters, respectively, in 30 minutes. And our past tests have indicated that the Coway Mighty, running on high for an hour, can reduce particulate pollution by nearly 100% in a typical bedroom, and then keep it there permanently on medium. Finally, in our 2018 “wildfire” test in Los Angeles, the Coway Mighty reduced a heavy load of incense smoke by 70% in 50 minutes—equaling the performance of some much more powerful competitors—in a room more than twice the size it is specced for.
On its high setting, the Coway Mighty can deliver 5.7 air changes per hour (ACH) in a 350-square-foot room with 8-foot ceilings, ensuring rapid cleaning in the event of a wildfire or other pollution emergency. On its “quiet,” or medium, setting it delivers 3 ACH, which keeps the air extremely clean under normal conditions.
The Coway Mighty has also demonstrated the ability to maintain its high performance for years, even as we’ve pushed its filters far beyond their stated one-year lifespans. We ran our original test model for two years without replacing the filter, and it still performed as well as it did on day one. We’ve had our current unit for nearly three years, and we’ve run it 24/7 the entire time. When we measured its performance in 2018 and 2019, each time on year-old filters, it again performed just as well as it did on day one, and it showed no difference in performance between the year-old filters and new replacements.
One of the keys to the Coway Mighty’s performance is its build quality, particularly the tight fit of its prefilter and HEPA filter. The prefilter captures large particles, like pet hair and lint, that would otherwise clog the HEPA filter and reduce its ability to capture fine particulates. The HEPA filter, meanwhile, fits snugly into the Mighty’s frame, sealing tightly against the plastic housing. That prevents air from bypassing the filter around the edges and ensures that virtually all air drawn through the machine gets HEPA-filtered, a design that’s a likely contributor to the Mighty’s excellent performance.
The Coway Mighty has a number of other qualities that make it very easy to live with—and that’s important for a device that typically runs 24 hours a day and lives in a bedroom, playroom, or living room.
At night, for example, you can shut off its display, which features a frankly far-too-bright “air quality indicator” lamp. The machine keeps running, and you get to sleep or watch TV in a nice dark room. (This said, we keep getting occasional reports from buyers who receive models that lack this function. In that case, we’ve learned that simply placing a US or Canadian quarter over the lamp completely blocks out its light, while letting you easily check the indicator if and when you want to.)
The Mighty is also very quiet. On the medium speed setting, we measured its noise output at just 39 decibels from a distance of 6 feet—a soft, fanlike whisper that’s easy to sleep or watch TV near.
And it’s light—a shade over 12 pounds—making it easy to move around via its convenient pocket handle.
Finally, it is compact, standing just 18 inches tall, 10 inches deep, and 17 inches wide, about the size and shape of a large beach tote. That puts it below “sight level,” and because it also tapers significantly from front to back it appears smaller than its dimensions suggest. Compared with tower-style purifiers we’ve tested, which have smaller footprints but are much taller, and compared with our large-space and VOC picks, which are monolithic, the Coway AP-1512HH Mighty—especially the white version—takes up less visual space.
Replacing the filters (an annual task for the HEPA filter, semiannual for the VOC) is easy: You simply unclip the front cover from the unit and pull the pre-, VOC, and HEPA filters out using their handy pull tabs. The prefilter is made of sturdy, fine plastic mesh, and you can vacuum or wipe it clean, or rinse it off under a faucet; do that every month or so to keep the machine performing optimally. The HEPA filters are clearly marked with the proper orientation, so there’s little danger of installing them incorrectly. There is, however, a common mistake any first-time air purifier user should watch for: leaving the plastic wrapper on the filter. Take that off.
Finally, the running costs for the Coway Mighty are easily the lowest we’ve found for a purifier of its abilities. On the medium setting, it draws just 8.1 watts, so running it 24/7 on that setting consumes just 71 kilowatts annually. At the February 2020 New York price of 20.1¢ per kilowatt-hour, that works out to a little more than $14 a year. Most states are cheaper. If you want to calculate for your state, the US Energy Information Administration lists the up-to-date rates.
Add in the annual replacement filters ($50), and the Mighty costs less than $65 a year to operate and about $470 over the course of five years, including the initial purchase price. In comparison, the similarly specced GermGuardian AC5900WCA, a 2019 competitor, consumes about $60 of electricity annually and needs a new $70 filter at least every eight months—so its five-year cost is about $900. Another way to look at it: You could buy and maintain two Coway Mighty units for less than the cost of some individual competitors. That’s not just a financial concern: Since air purifiers perform best when cleaning a single room, it’s worth considering separate machines for, say, the bedroom and the living room.
Flaws but not dealbreakers
In early fall 2020, we received a few notes from readers about a pair of issues with their Coways. Similar comments have been showing up sporadically in recent customer reviews on Amazon and other retail sites.
The first is an imbalanced fan, which causes the whole unit to shake uncontrollably and in some cases leads the fan to self-destruct. We asked Coway about this, and a spokesperson replied that Coway is aware of the issue and working on strengthening the fans’ balancing mechanism. In the meantime, customers with this issue can get a free replacement from Coway.
The second is a strong odor coming off of new replacement filters. Coway believes that the issue stems from the wildfires out West—that smoke is infiltrating mail-distribution centers and causing the filters to pick up smells during storage and transit. Again, the company says it will send free replacements, but adds that the extraordinarily high demand for air purifiers this year (due to the fires and COVID-19) is stretching its customer service department, so response times may be slower than normal.
Although Coway added a display-shutoff function to the AP-1512HH Mighty in December 2018, a few Wirecutter readers have received old units, which lack the shutoff, as late as September 2019. If that happens to you, and if you ask, the retailer should replace the unit. Or you can do what guide author Tim Heffernan does on his old test unit: Put a US quarter over the bright air-quality indicator lamp. That way you can easily check the lamp when you want to and keep it blocked the rest of the time. (A Canadian quarter also works.)
It is too easy to begin operating an air purifier without first removing the plastic wrapping the filter comes in. The reason it’s an easy blunder is that the filters come shipped inside the unit, so you may never see them—it’s tempting to just “plug and play.” Almost all air purifiers arrive with their filters wrapped, and almost all have stickers on the machine or warnings in the brochure to remove the wrappers, but the frequency at which we’ve heard of this mistake from readers and co-workers merits a special mention here, since the Coway Mighty is our top pick.
Like many air purifiers, the Coway Mighty has an ionizing function in addition to its HEPA filtration. We recommend leaving the ionizing function off. The effectiveness of such features is dubious, and it draws additional electrical power. (On this model, you can tell that the ionizer is off when the button is unlit.) If you do choose to use the ionizer, you will be happy to know that it is certified by the California Air Resources Board not to produce ozone in excess of the 0.050-parts-per-million limit.
One trend we’ve encountered in the scant negative reviews of the Coway Mighty concerns complaints about nonresponsive customer service. However, as you can see on this review of a malfunctioning unit, Coway responds in the thread. So reaching representatives may not be as easy as it should be, but they are out there and listening—at least to the negative public-facing reviews.
Coway has a support center based in Austin, Texas; you can reach it at email@example.com or 888-960-5747.
Runner-up: Coway Airmega 200M
The Coway Airmega 200M is virtually identical to our top pick, the Coway AP-1512HH Mighty. They are made by the same company, and they are physically so similar that their faceplates and filters are interchangeable. The Airmega 200M has a slightly more powerful motor, which accounts for its marginally better performance in our tests: In a half hour running on its highest setting, it reduced particulates by 99.4% on new filters, versus the Mighty’s 98.9%, and by 99.1% on old filters, versus the Mighty’s 98.9. These differences are so small as to be functionally meaningless, and in any case favor the Airmega 200M. In our three-hour test of the Mighty, that machine reduced a heavy load (15 matches’ worth) of smoke by 99.9% in the first hour on high and maintained that level for the next two hours on medium. We believe that the Airmega 200M, with its nearly identical design, interchangeable filters, and slightly more powerful motor, would undoubtedly perform at least as well.
The Airmega 200M shares the Mighty’s display-shutoff feature, which we value highly because it turns off the overly bright air quality indicator lamp and makes this model much more conducive to bedroom use. Visually, the Airmega 200M differs from the Mighty in that it has a square grille instead of a round aperture; like the Mighty, it’s available in both black and white versions. Previously, we dismissed the Airmega 200M because it was significantly more expensive, but the prices of this model and the Mighty have evened up recently. We advise anyone debating between them to compare their prices (and appearances) and purchase whichever model you prefer. We recommend both just as highly.
Upgrade pick: Blueair Blue Pure 211+
If you need to purify the air in a seriously large space, we recommend the Blueair Blue Pure 211+. It’s extremely powerful, delivering our recommended 4 ACH (air changes per hour) in spaces as large as 655 square feet (assuming an 8-foot ceiling). That means it can clean the combined living areas of many open-floor-plan homes. And the Blue Pure 211+ is far less expensive over five years—$700 to $800, including both the up-front cost and the annual cost of electricity and replacement filters—than most large-space purifiers. Last, it’s an attractive, quiet-running machine, so it’s easy to live with. All that said, unless you really need to clean an especially large space, the even quieter, smaller, and more affordable Coway AP-1512HH Mighty is a better choice.
In just 30 minutes, the Blue Pure 211+ reduced a heavy load of 0.3-micron smoke particles by 99.3% and 98.4% on high and “quiet”/medium, respectively, in our 2019 test, with filters that had seen eight months of 24/7 use. With new filters, it reduced them by 99.3% and 99.2%, respectively. Those results made it one of the most efficient purifiers we tested, as well as one of the most consistent on different settings. (By comparison, our top pick, the Coway Mighty, dropped from 98.9% reduction on high to 87.7% reduction on medium.)
The Blue Pure 211+ is alone among our picks in not being true HEPA. However, it has excellent Clean Air Delivery Rate (CADR) certifications from the Association of Home Appliance Manufacturers, which in some ways is a more rigorous measurement. (Read more in How we picked.) And it has always delivered exceptional performance in our testing at the 0.3-micron HEPA standard, on both new and year-old filters.
It delivers a consistent, quality performance for several reasons. First, it pulls a lot of air through its filter each minute. With a CADR of 350 cubic feet per minute on high for smoke, pollen, and dust, it handily outdraws most purifiers in its price range and many machines that cost far more. On its “quiet”/medium setting, it delivers CADR 231 performance for smoke, pollen, and dust—roughly what the Coway Mighty delivers on high. In a 500-square-foot space with 8-foot ceilings, that means it makes 5.3 air changes per hour on high, well above our 4 ACH threshold. And on medium, it reaches a rate of 3.5 ACH, more than enough to keep the air clean under normal conditions.
Second, the Blue Pure 211+, like all Blueair purifiers, employs a unique mechanism to boost its performance. The machine imparts an electrical charge to any particles that initially pass through its filter. When these particles then pass through the machine a second time, the charge helps them stick to the filter fibers, similar to the way a staticky sock sticks to other fabric in the dryer. That may help explain why the Blue Pure 211+ offers nearly identical filtration on both its high and “quiet” fan speeds. (This mechanism is distinct from the ionizers found on many purifiers, including the Coway AP-1512HH Mighty; they charge air molecules directly.)
In 2018, we declared the Blue Pure 211+ “the stiffest competition we’ve found for the Coway AP-1512HH Mighty,” our long-standing top choice for general use. But having lived with this Blueair model for a year, we now think it’s best for large spaces specifically. It’s physically quite a bit larger than the Mighty, both in height and footprint, and in a bedroom, playroom, or living room it can be a visually imposing presence. It’s also a bit louder, at 43 versus 39 decibels on the everyday medium setting. Both of those numbers fall well below our 50-decibel limit for “quiet,” but the difference is readily audible, especially when you’re going to sleep or watching TV. It’s a fanlike white noise, so not unpleasant, but if you are particularly noise-sensitive it’s something to bear in mind. And when the machine is running, its on/off button emits a glow that you can’t turn off, so if you’re bothered by lights when trying to sleep (as guide author Tim Heffernan is), it can be an annoyance. Last, on the two machines’ everyday, medium fan settings, the Blue Pure 211+ draws a lot more power than the Mighty: 46.8 watts versus 8.1. That’s 1.1 kilowatt-hours a day, 33 kWh per month, or 410 kWh per year for this Blueair model versus 0.2, 6, and 73, respectively, for the Coway. If you’re using a Blue Pure 211+ to purify a space that the Coway AP-1512HH Mighty can handle, that’s a lot of wasted electricity.
However, compared with the other large-space purifiers we’ve tested, the Blue Pure 211+ is comparable in five-year cost. Including its typical up-front price of $300 and $850 in electricity and filter replacements (which are recommended every six months), it will set you back about $1,150 over that period. (That’s based on running the machine 24/7 on medium, and paying New York’s high electricity rates.) That makes it very close to our former top pick, the Coway Airmega 400, at about $1,200. The two machines are similar in power and noise output too, and they performed almost identically in our 2019 testing. The Austin Air HealthMate HM400, our pick for VOC removal, is also powerful enough to clean large spaces. But it costs about the same to buy and run for five years (roughly $1,200), and it’s louder, larger, and less attractive than the Blue Pure 211+. We really like the five different-colored prefilter “skins” you can choose from to cover the 211+, and you can also run the machine bare for a minimalist look. (Note that we installed the pink skin in our photos incorrectly—it‘s meant to be tucked behind the control knob, creating a seamless appearance.)
Budget pick: Levoit Core 300
Our budget pick, the Levoit Core 300, is meant for smaller bedrooms or offices about 200 square feet in size. In such spaces, it performs impressively. In our 2020 test, it reduced a heavy load of smoke in our 135-square-foot test space by 97.4% in half an hour on high and 92.6% on medium. Capable of 6.75 air changes per hour (ACH) in a bedroom-size 150-square-foot space, it far exceeds our 4 ACH minimum. And with a typical up-front cost of $100, it’s the cheapest of our picks to buy. But it’s not especially energy efficient, consuming about $61 of electricity (albeit at New York’s steeper prices) when run 24/7 for a year. This raises its five-year running cost to about $480 (electricity plus seven replacement filters, based on its recommended eight-month replacement cycle). That aside, it's a compact, attractive machine, and its display-shutoff feature (which turns off the bright LED control panel) makes it especially suited for bedrooms. The Core 300 replaces our former budget pick, the Blueair Blue Pure 411, which was considerably outperformed by the Levoit.
On the high setting (which we measured at 54.1 decibels—too loud for sleep, and far above our 50-decibel limit for comfortable conversation), the Levoit Core 300 reduced particulates in our 135-square-foot New York test room by 97.4% in 30 minutes. On medium, where it produces a sleep-friendly 43.2 decibels, it achieved an impressive 92.6% reduction. (Compare that with the Blue Pure 411’s measurements: 87.2% on high and 70.7% on medium.) But surprisingly, the Core 300 also measured a bit better than the top-pick Coway AP-1512HH Mighty on medium (87.6%). We believe this result is anomalous, and likely due to variations in the initial test conditions (we measured the Core 300 in a separate round of testing). The fact is, the Core 300 has much lower airflow than the Coway—a 135 CADR versus the Coway’s 240—and will not be adequate for the living-room-size spaces where the Coway excels. It simply doesn’t move enough air to work effectively in anything bigger than a bedroom.
The Core 300 is easy to live with for a few reasons. It’s quite small at 14½ inches tall and 8½ inches wide, so it fits on a bedside table or the corner of a desk. On its medium and slow speeds, it’s quiet enough for sleeping or conversing near (43.2 decibels on medium and 38.7 on low, measured from 6 feet away). You can shut off the display so that it emits no light, a feature it shares with the Coway Mighty, which makes it much easier to sleep near. The Core 300 also features a separate “sleep mode,” at which it produces almost undetectable levels of noise—but also moves so little air that we doubt it does much for purification. The medium and low settings should be quiet enough to sleep near for most people.
At about $100, the Core 300 is inexpensive upfront, but it is not a very energy-efficient purifier, especially for its size. The Core 300 draws 34.6 watts on medium (and 31.8 watts on low), while the much more powerful Coway Mighty draws just 8.1 watts. Running the Core 300 on medium speed 24/7, you’ll consume about 303 kilowatt-hours per year; at New York’s rates that works out to $61 annually. And the filters need to be replaced every eight months, at about $25 a pop. So over the course of five years, its running costs may be as much as $480—far more than the Coway’s roughly $270.
Still, that works out to a manageable $7.50 a month, and the Core 300’s low up-front cost is easier to swallow than the Coway’s typical $200. if you need to clean the air in a small space—a bedroom, office, or dorm room up to about 200 square feet—it’s a solid choice. We’ll continue to test and rate small-space purifiers later in 2020, when we anticipate having access to our New York test space again.
Also great: Austin Air HealthMate HM400
This model’s HEPA filter removes particulates (like pollen and smoke) from the air, and its second filter efficiently removes odors and VOC gases—an ability many purifiers lack.
If you live in an environment with high levels of both particulate pollution and volatile organic compounds (such as near a farm where biocides are sprayed, a chemical or power plant, or a refinery), we recommend the Austin Air HealthMate HM400. Like our other picks, it uses a true HEPA filter that efficiently captures particulate pollutants such as pollen and smoke. But unlike them, it also employs a truly effective adsorbent filter that efficiently captures gaseous pollutants, which include volatile organic compounds (VOCs) like formaldehyde—a common component in the glues and foam padding used to make furniture—and, more broadly, odorous gases like those produced by pet urine and car engines. Most of our picks have token adsorbent filters, amounting to a few ounces; in contrast, the HM400 has 15 pounds of adsorbent. In our past testing, it reduced a heavy load of ethanol vapors to 13% of the starting point within 20 minutes; the nearest competitor we tested did only half as well, and the rest were marginally or simply not effective. Its exceptional performance in this area is a big part of why FEMA and the Red Cross chose Austin Air units for deployment at Ground Zero and the surrounding areas in the aftermath of 9/11.
When it comes to particulate pollution, the HM400 is a solid performer, reducing particulates to less than 20% of starting levels after 30 minutes on high in our 2017 real-world test (fourth best in our high-setting test) and to 50% (joint third best) on low. But it’s not as fast or efficient as our top pick, the Coway AP-1512HH Mighty; the dense VOC filter means this machine works slower and consumes more electricity. The HM400 is also notably loud, maxing out at 58 decibels on high.
And its performance comes at a steep price: The HM400 typically costs more than $500 up front—although price can vary based on color, sometimes by as much as $100—and replacement filters usually cost a bit more than $200. That said, the filters are designed to last five years, so the replacement cost doesn’t factor into the first five years of ownership. Based on 24/7 use on the medium speed, where the HM400 consumes 81.8 watts, its five-year running costs (at New York’s high rates) are about $720. That’s about three times the five-year running cost of our top pick, the Coway Mighty. Factoring in their purchase prices as well as running costs, the HM400 and our pick for large spaces, the Blue Pure 211+, cost about the same over five years (about $1,200 versus $1,150).
If you simply need to remove particulates from your air in a large space, the Blue Pure 211+ is easier to live with—it’s quieter, smaller, and better looking, which is why it’s our main pick for large spaces. If you have specific concerns about VOCs, the HM400 is by far the best portable air purifier we’ve ever found.
What if you just put a furnace filter on a box fan?
In 2018, guide author Tim Heffernan tested a popular claim: that sticking a furnace/HVAC filter on a standard box fan produces a useful DIY air purifier. He taped a 20-by-20-inch Honeywell FPR 9 filter to a 20-inch Lasko box fan and ran that combo through the standard 35-minute, five-match test in the 200-square-foot New York space, with the fan on high. And you know what? It did okay, cutting the initial particulate load by 87% over 35 minutes on medium. That’s nothing like the 99% reductions our picks achieved on their high settings, and it didn’t reduce particulates as quickly, but the results were better than one might expect.
Some caveats apply: Tim was careful to seal the filter around its entire perimeter with clear pro-strength packing tape—any gap would have let unfiltered air pass through, same as on dedicated air purifiers. You should do the same if you try this hack. And no box fan is engineered to withstand the extra workload of driving air through a dense filter, so we can’t claim this won’t damage the fan’s motor, and we wouldn’t consider it a long-term solution for air-quality issues. But if you have an air-quality emergency on your hands—regional wildfires, or your charred dinner under the broiler—and you have a box fan, tape, the right sort of filter, and no time to buy an air purifier, it’s worth a shot.
One other thing worth mentioning: A popular video of this hack, from the University of Michigan Health System, overstates its potential. The presenter places the particle counter directly in front of the filter—almost touching it with the sensor—and notes that virtually no particles are passing through. Well, duh: Any air that passes through a HEPA or medium-MERV filter will be virtually particulate free. It’s far more important to measure the effect of a filter on the overall particulate load in the room. After all, you won’t be sitting or sleeping with your face against your purifier. That’s why we’ve always measured purifier performance at a considerable distance from the machines, outside of the path of the cleaned airflow.
What settings should you run an air purifier on?
We have long recommended running air purifiers on high for an hour and thereafter running them on the “quiet”/medium setting to create and maintain clean air in the home. But we had originally extrapolated this claim from our past discrete 20-, 30-, or 60-minute test results on each setting, so in 2018 we specifically tested it on the Coway AP-1512HH Mighty and Airmega 400 over the course of three hours—one hour on high, followed by two on medium—after burning 15 wooden matches to create an initial heavy load of fine smoke particulates.
The Mighty reduced the particulate concentration by 99.9% in the first hour, on high. Over the next two hours on medium, the particulate load remained stable, varying no more than 0.1%. The Airmega 400 also reduced the particulate concentration by 99.9% in the first hour on high, and thereafter the particulate load varied by no more than 0.2% on medium.
These results back our claim that running a purifier on high for an hour, and thereafter on medium, creates and maintains extremely clean air inside a home with the windows and other entryways closed under normal conditions, including a temporary initial spike in pollution (such as a neighbor’s barbecue, or a product tester burning matches).
That said, after we created the abnormal smoke conditions at the outset of the tests, from then on the New York test room was subject to only the natural, ambient air conditions and whatever leakage infiltrated the test room. So we deliberately countered that setup in our Los Angeles office, where we tested our top pick, the Coway AP-1512HH Mighty, and our large-space pick, the Blueair Blue Pure 211+, in handling ongoing smoke from burning incense sticks. And in that test, we learned that we had to run them on high to get meaningful purification (which both models achieved, cutting the particulates by half or more in 50 minutes).
Here’s the takeaway: In the case of a nearby wildfire or other ongoing pollution crisis, where ambient local air conditions are continuously bad, keeping your air purifier on high is probably the best practice. It may be disruptively noisy, but that’s a small and temporary price to pay for clean air.
How HEPA filters work
HEPA stands for high-efficiency particulate air. The technology is the result of an industrial need that became critical in the Atomic Age: high volumes of very clean air, vital for the production of microprocessors and other sensitive instruments. Happily, HEPA filtration is also fundamentally simple and cheap, which means it’s available to everyone today.
HEPA filtration is a physical process: A fan running at high speed draws particles suspended in the air through a dense, feltlike filter with gaps of varying size. The fibers in a HEPA filter capture airborne particulates in three basic ways (PDF). The largest of the particulates, about 0.5 micron and above, are captured via impaction: Unable to change their course due to momentum, they simply slam into the fibers and stick to them. Particles less than 0.5 micron, but not too much less, are captured by interception: Their lower momentum allows them to flow around some fibers, but eventually they come close enough to touch one fiber on the way by, and again they stick. Finally, very fine particles, namely those below 0.1 micron, or at most one-fifth of the diameter of the fibers, get bounced around randomly and slowed by their interactions with atmospheric atoms and molecules, and eventually drift or get bounced into a filter fiber, whereupon (yet again) they stick; this process is called diffusion. The net result is that virtually all particles get captured quickly, while airflow is only slightly impeded.
Crucially, the hardest particles to capture are what you might call the Baby Bears: At 0.3 micron, they’re at the low limit of interception momentum and above the limit of diffusion—in other words, they’re “just right” to get through a HEPA filter. The solution is to make the filter dense enough that it has a sufficient amount of fibers to capture most of the 0.3-micron particles. And again, according to the US HEPA standard, “most of them” means 99.97% of them in a single pass.
Molekule Air and Air Mini: The worst air purifiers we’ve ever tested
In the summer of 2019, we purchased a Molekule Air (the flagship model) and tested it. We bought an Air Mini that fall and tested it in February 2020. At the time we tested the Molekule Air, the company claimed that its “scientifically-proven nanotechnology outperforms HEPA filters in every category of pollutant.”
Our tests proved otherwise. And by mid-2020, that language had been withdrawn, after many of the company’s claims were ruled against in a case before the National Advertising Division and upheld in a later appeal before the National Advertising Review Board. The Molekule Air turned in the worst performance on particulates of any purifier, of any size, of any price, that we have tested in the seven years that we have been producing this guide. The Air Mini outperformed it, but that’s not saying much: It still gave the second-worst performance we’ve ever seen.
Guide author Tim Heffernan asked Molekule CEO Dilip Goswami why the language was removed. He answered, “The point about ‘in all categories’ is that we see a device that outperforms across all of the categories. Right? So we’re not trying to say that individually, on any particular metric, we would be number one. Right? What we’re saying is, when you look across all the categories, we outperform HEPA. Right? And that’s what we’re attempting to convey with that. And so—it’s fair to say that we needed to re-examine some of the language to make sure that it’s saying what we’re intending to say.”
The NAD and NARB cases made clear that this was an understatement: All of Molekule’s quantified claims about the Air’s performance; all of its claims about superiority to HEPA; all of its customer and doctor testimonials about the ability of the Air’s filter to reduce asthma and allergy symptoms; and many of its claims to have been independently tested, were ruled unsupported. Other claims were ruled too broad.
The Molekule Air uses a proprietary mechanism to remove particles from the air, which the company terms PECO: photo electrochemical oxidation. It’s a derivation of an older technology, PCO (photocatalytic oxidation). Briefly summed up: PECO and PCO use the excitation of titanium dioxide by UV light to produce hydroxyl radicals (OH, one oxygen and one hydrogen atom bound together). Hydroxyls are highly reactive, and they rapidly combine with nearby materials. If they encounter a hydrogen atom, they combine to produce water (H2O). If they encounter other substances, including VOCs and airborne particles, they may react with and break up or otherwise alter them. As such, both PECO and PCO are completely distinct from HEPA filtration, which physically captures most airborne particles but does not capture VOCs or other molecular-scale pollutants. However, the Air and Air Mini also employ a physical prefilter—the Air’s rated MERV 13, per the NARB report, meaning not far below HEPA filters in efficiency—to capture particulates.
We conducted the same tests on the Molekule Air as we did on the HEPA-filtration competitors, taking baseline readings, burning five matches to create a mass of fine airborne particulates, and then measuring the reduction in those particulates over the course of 30 minutes on all three of the machine’s “speed” settings (called Silent, Auto, and Boost, akin to low, medium, and high). We also tested the Molekule on its Dark setting, in which its light-based, primary PECO purification system is shut off and only its physical prefilter is in use; we set the airflow to Auto on the Dark tests.
We conducted each of our tests twice. First, we tested the Molekule exactly as we tested the HEPA purifiers: Using the ambient air conditions in the room, plus whatever particulates the burned matches added at the outset, we ran it on the four settings and recorded the particulate reduction after a half hour. But unlike the HEPA purifiers, all of which proved capable of deeply cleaning the air, the Molekule left the air heavily loaded with particulates on every setting. So we ran a second round of tests on the Molekule with the starting conditions as clean as possible. We achieved this by running the powerful Medify MA-112 purifier on high for 15 minutes before each test, reducing the particles per cubic foot from millions to less than 10,000. That’s very, very clean air. In describing test results below, the word ambient means that we started purifying the air as we found it—the usual process—and the word clean means we brought in the Medify to reset the conditions for the Molekule’s next test. To be clear, no other machine in our tests received this handicap.
Let’s start with the Molekule’s strongest performance. On its Boost setting—when it was moving the maximum amount of air it could—the Molekule reduced 0.3-micron particulates by 61.3% under ambient starting conditions and 57.0% in clean starting conditions. In both cases those numbers were worse than what our budget pick for small rooms, the Blueair Blue Pure 411, produced on its medium setting with new filters: 70.7% removal. (On high, the Blue Pure 411 achieved 87.2% reduction.) The Molekule was not remotely comparable to the Coway AP-1512HH Mighty or the Blueair Blue Pure 211+, which reduced particulates by 98.9% and 99.3% on their high settings and by 87.6% and 99.2% on medium, respectively.
On Auto (akin to medium—the Air does not contain a particle counter to adjust to air conditions; rather, you input your room’s rough size and the machine picks a fan speed Molekule considers adequate), the Air performed worse, reducing 0.3-micron particulates by just 18.0% (ambient) and 26.4% (clean). On Silent, it performed worse yet, reducing 0.3-micron particulates by 6.5% (ambient) and 7.2% (clean). And on Dark plus Auto, with its primary PECO purification system shut off and its fan on the equivalent of a medium setting, it reduced them by 21.3% (ambient) and 18.0% (clean). Interestingly, those numbers closely mirror our results on the Auto setting with the PECO system turned on, suggesting the possibility that the Molekule mostly relies on its physical prefilter, not its proprietary PECO mechanism, to eliminate particulates.
At a certain point, these results look worse than what you see with no purifier running at all. In a pair of baseline background tests, which we use as a control measure, 0.3-micron particulate levels dropped by 13.9% and 15.3% on their own. That’s due to settling, in which particles fall to a room’s surfaces; agglomeration, in which two or more particles naturally combine to form a single particle; and ambient ventilation, which we standardized for all our tests. One possible reason the Molekule performed worse than background reduction is that its fan stirred up the air and kept particles from settling.
In our years of testing, one dead-simple measure has proven to be a good proxy for a purifier’s performance: the volume of air it can move. Hence our emphasis on air changes per hour. Despite our repeated requests (and co-CEO Dilip Goswami’s stated willingness to do so), Molekule never shared its airflow numbers (cfm, or cubic feet per minute). But now-withdrawn company literature gave us an an idea of its volumetric limits: The company used to claim the Air provides “a full replacement” of the air in a 600-square-foot room in “under an hour” (and elsewhere “every hour”), and in a 150-square-foot room in “under 15 minutes.” That suggested that the Air has a maximum ACH of around 4 in a 150-square-foot room with 8-foot ceilings. In fact, by our later reading of the company’s testimony in the NAD case, the Air is even weaker: Molekule listed an airflow rate of 90 cfm, which we assume is the maximum—that’s how all other air purifiers state their numbers.
Regardless, the Air is weak. An ACH of 4 in a 150-square-foot room is two-thirds of what our budget pick, the Blue Pure 411, can achieve in a space of those dimensions, less than a fifth of what our top pick, the Coway Mighty, can achieve, and barely an eighth of what our large-space-pick, the Blue Pure 211+, can achieve.
These findings all mean that the Molekule is not remotely worth its high price: usually $800 up front, versus a typical $200 for our top-pick Coway AP-1512HH Mighty, a much more capable machine on particulates. The numbers get worse when you factor in running costs: five years of running the Coway on medium and replacing the filters on schedule will max out at around $265, and less if you don’t pay the high New York electricity rates we base our calculations on. The Molekule’s comparable cost is about $1,350. Last, on top of the machine’s weak performance and high cost, we found the Molekule app persistently laggy. And the unit’s always-on blue glow—which indicates when its primary PECO filter is in operation—can disrupt sleep. (You can’t physically block the glow with a coin or tape, because doing so would block the Molekule’s delivery of air.)
Throughout its promotional literature, Molekule used to claim its PECO technology “completely destroys” particulates in the air and contrasted this to HEPA purifiers, which, the company said, can’t capture viruses or anything else smaller than 0.3 micron (in fact, they can and do); release mold and bacteria back into the air (they don’t); and can’t capture VOCs (true of HEPA filters—but their secondary VOC filters can). It agreed to withdraw these claims as part of the NAD/NARB cases, because they’re untrue.
It also agreed to withdraw its longstanding tagline, “Finally, an air purifier that actually works.”
We tested the Molekule Mini in much the same way in February 2020, in the same 135-square-foot, 1,215-cubic-foot New York office. Based on our tests of the Molekule Air, we forewent the “ambient” testing and instead granted the Mini the same handicap of “clean air” tests, reducing the match smoke between tests with our pick for large spaces, the Blue Pure 211+.
On its highest setting (speed 5), the Mini did well, reducing the smoke from five wooden matches by 96.2% in half an hour. But at that speed the Mini produced an ear-splitting 66.3 decibels of high-pitched fan noise, measured from 6 feet away—completely unlivable in any living space, let alone the small spaces Molekule intends the Mini to be used in. (You can hear for yourself how loud it is in this video from the Sleep Sherpa. In our office, even at a distance of 50 feet, the noise was intrusive during conversation.)
On speed 4, the Mini still produced 56.5 decibels, far above our 50-decibel limit for comfortable living.
It fell below that limit, to 45.4 decibels, on speed 3. That’s louder than our picks for large, standard, and small spaces on their “quiet”/medium speeds. And at that speed, the Mini’s performance on particulate removal tanked: It cut the match smoke by just 63.3% in 30 minutes.
On its lowest and quietest setting (speed 1; 33.1 decibels), the Mini’s filtration performance dropped further, reducing the smoke by 60.3% in 30 minutes.
These results rank the Molekule Mini as the second-worst air purifier we have ever tested, behind—you guessed it—the other Molekule. We attribute the Mini’s superiority to the Molekule Air to its much bigger physical prefilter: It’s about five times larger by area than the Air’s. Put another way, the Mini’s PECO filter, which appears identical to the Air’s, doesn’t seem to make much difference on particulates.
Finally, the Air Mini’s cost-to-performance ratio on particulates puts it badly behind our small-space pick, the Levoit Core 300. The Mini typically costs $400, versus $100 for the Levoit. And its running costs are much higher too. The Mini needs a $75 replacement filter every six months; over five years (nine replacements), that works out to $675. Five years of electricity, assuming the unit runs 24/7 on speed 3 (medium), adds an additional $165 (at New York’s high rates). The Levoit costs a bit more than half as much for the same upkeep—and, of course, roundly outperforms the Air Mini, as well.
At a cost of $1,000, the Aeris Aair 3-in-1 Pro is a high-end purifier—a growing category that we plan to explore in depth in the future. In addition to its HEPA filter, it contains a large VOC filter composed of 2.2 pounds of activated carbon and alumina. That should make it far better at capturing VOCs (odors and other gases) than the tiny VOC filters most purifiers contain. The HEPA filter is also treated with an antibacterial coating that, Aeris says, “reduces risks of infection when replacing filters.” (That risk is already extremely low, as HEPA filters are not a conducive environment for bacterial growth to begin with.) But while it tested well, the Aair did not perform any better on particulates than our much less expensive pick for large rooms, the Blue Pure 211+. The Aair reduced particulates by 98.1% and 94.1% on high and medium in our 30-minute tests; the 211+ achieved 99.3% and 98.4% reductions in identical conditions. Another knock on the Aair: The filters last only six months, and replacements cost $200.
2019 tests and contenders
The Blueair Blue Pure 411, our former budget pick, performed well for a small-space purifier and is exceptionally energy efficient. Running on medium 24/7, it only consumes about $6 of electricity per year. Replacement filters every six months, at $22 apiece, will cost $198 over the course of five years (nine new filters). That makes it far cheaper to own than our new top pick for small spaces, the Levoit Core 300, which may cost $480 over five years for filter replacements and electricity. However, performance is our most important measure of a purifier, and the Levoit far outperformed the Blue Pure 411. We will be testing the new, slightly more powerful Blue Pure 411+ once we have access to our New York office again.
In 2019, we tested two of Dyson’s latest-generation air purifiers, Pure Cool TP04 and Pure Hot+Cool HP04. Of them, the TP04 performed better, but neither measured up well against our top pick, the Coway AP-1512HH Mighty, and our large-space pick, the Blueair Blue Pure 211+. On its highest setting, the TP04 reduced particulate pollution by 86.6% in 30 minutes; compare that with 98.9% and 99.3% from the Mighty and the Blue Pure 211+, respectively. On medium—which we set as fan speed 6 of the 10 speeds available—the TP04 managed just 74.4% reduction. The Coway and Blueair scored 87.6% and 99.2%, respectively. The Dyson Pure Hot+Cool HP04, which incorporates a space heater as well as a purifier, in theory should have performed somewhat better than the TP04 because it can move a slightly greater volume of air. But in our tests it performed significantly worse, achieving just 77.4% and 55.1% reduction on its highest and medium (speed 6) settings, respectively. We cannot recommend either Dyson purifier, especially given their high price relative to those of our much higher-performing picks. We have also found no evidence that the machines’ fan function, as Dyson claims, makes them superior to other purifiers in the distribution of filtered air throughout a room. In fact, our years of testing have shown that any appropriately sized purifier will distribute filtered air evenly, into the farthest corner of a room.
We have not tested the Dyson Pure Hot+Cool HP06 Cryptomic purifier, but spoke at length with a Dyson engineer and representative about it. In terms of particle filtration, it is virtually identical to the Pure Hot+Cool HP04 (see preceding paragraph), using the same HEPA filter and featuring only marginally lower airflow. We would not recommend it for same reasons we do not recommend the HP04. The HP06 adds a molecular formaldehyde filter, which Dyson calls the Cryptomic.
We tested two purifiers from Medify, the MA-40 and the MA-112. The smaller Medify MA-40 has specs similar to those of our top pick, the Coway AP-1512HH Mighty, and in fact it achieved the same reduction in particulate pollutants: 98.9% on high. It’s also a good-looking and well-built appliance, with a glass touchscreen (not plastic as on most purifiers). But it’s a loud machine, measuring 52 decibels (above our 50-decibel definition of “quiet”) on its medium setting and 42 on low. For comparison, the Coway Mighty measures 39 decibels on medium and 31 decibels (nearly inaudible) on low. Typically, this Medify model also costs about $100 more than the Coway.
The huge and exceptionally powerful Medify MA-112 has the highest CADR rating we’ve ever seen: 950. (That’s almost three times more cubic feet per minute than with our large-space pick, the Blueair Blue Pure 211+.) It virtually eliminated particulates from our test room, reducing them by 99.9% on its high and medium speeds. And for such a powerful machine, the MA-112 is surprisingly easy on the ears, registering as “quiet” on its low, low-medium, and high-medium speeds (39, 42, and 47 decibels, respectively). But this model is physically huge, at 28 inches high and 15 wide, and it’s a rare home that has an open space big enough to demand such a powerful purifier (Medify says casinos use it to clear cigarette smoke). It has historically cost upwards of $750; we have seen it dip to near $500 at times, which is closer to being competitive with our other picks, but again: only if you really need to clean a vast space.
The GermGuardian AC5900WCA was a stellar performer in our 2019 test, reducing particulates by 99.3% on high and 98% on medium. Those results actually beat the performance of the similarly priced Coway AP-1512HH Mighty, our top pick, despite the GermGuardian’s slightly lower CADR numbers. And we like the GermGuardian’s clean looks and clever night-light feature: a small blue circular LED that glows through the machine’s seamless white faceplate. (You can turn the night-light and the display lights off if they disrupt your sleep.) But we also found it to be much louder than the Mighty, measuring 47 versus 39 decibels on its “quiet”/medium setting, and the quality of the sound was rough and whooshy, versus the Mighty’s steady white noise. This model is far more expensive to run, as well, requiring a $70 replacement filter every eight months (versus $50 once a year for the Mighty) and using about $64 versus $14 of electricity annually if run 24/7 on medium, due to its much higher energy consumption. Over five years, the GermGuardian will cost roughly $900 versus the Coway’s roughly $470. Note: The AC5900WCA is widely out of stock as of July 2020, but the company is producing more units and expects to have them available later in the summer and this fall.
The Levoit LV-H133 is another competitor to the top-pick Coway, and it produced similar test results—98.8% and 92.9% reduction in particulates on high and medium, versus 98.9% and 87.6%. But it’s more expensive up front and over the course of five years’ upkeep, and its taller form and higher noise output make it visually and audibly intrusive.
The Levoit Vista 200 is a small-space machine, and it’s one of the best-selling purifiers on Amazon. However, it’s much weaker on CADR specs than our small-space pick, the Blueair Blue Pure 411, and it produced very poor results in our tests: just 58.0% and 59.2% reduction of particulates on high and medium, respectively, versus the Blue Pure 411’s 87.2% and 70.7%.
Our previous top pick among large-space purifiers, the Coway Airmega 400, is a stellar performer, registering 99.9% and 99.7% reduction of particulates on high and medium, on both new filters and filters that had been run 24/7 for a year. Those figures slightly topped the results from our current large-space pick, the Blueair Blue Pure 211+, which came in at 99.3% and 99.2% on new filters and 99.3% and 98.4% on filters that had been run 24/7 for eight months. The two machines are similarly quiet, with the Airmega 400 registering 40 decibels on its “quiet”/high-medium setting and the Blue Pure 211+ measuring at 43 decibels on medium. But the Blue Pure 211+ came out on top in long-term costs: It typically sells for $250 versus the Airmega 400’s $450 to $550, and the Blue Pure 211+ totals about $800 over five years versus about $1,100, counting the cost of annual replacement filters and electricity.
While we were researching and writing this guide, LG discontinued its Air Purifier Tower AS401WWA1 and PuriCare Air Purifier Round Console. Some units may still be available as dead stock, but the world needn’t lament the fallen. The Tower had much lower specs than our top pick, the Coway AP-1512HH Mighty, yet it cost $400—more than twice as much. The Round Console was also weaker on specs and higher priced than the Coway, at $300.
The Inofia PM1320 claims to work in rooms as large as 800 square feet. Based on its specs, it’s appropriate for rooms of just 287 square feet (where its CADR numbers result in our recommended 4 air changes per hour).
The Pure Company’s Large Room Air Purifier usually costs $400 but has lower specs than those of our typically $175 top pick, the Coway AP-1512HH Mighty.
The Levoit LV-H134 also costs about $400 and has lower specs than the top-pick Coway.
Although the Winix FresHome P150 is similar in physical size to the Coway AP-1512HH Mighty, it has specs well below those of a small-space purifier.
Winix’s HR900 Ultimate Pet Air Purifier has far lower specs than that model and our less expensive top pick, the Coway AP-1512HH Mighty.
We find tower-style machines like the Winix NK100 to be visually intrusive. The NK100 also has lower specs than the top-pick Coway Mighty and typically costs a bit more. The otherwise identical Winix QS and Winix NK105 add dubious features (a Bluetooth speaker and Wi-Fi connectivity, respectively), and both of those models usually cost more than the Coway.
The Hathaspace Smart True HEPA Air Purifier has solid reviews and costs a bit less than the top-pick Coway. For that price, though, you get a machine that’s barely a third as capable: The Hathaspace delivers 2 air changes per hour in a 350-square-foot room, whereas the Coway delivers 5.7.
Dyson calls the Pure Cool Me BP01 a “personal purifying fan”—it’s designed to deliver a focused stream of air onto a person’s face from a bedside table or an office desk—and does not consider it a whole-room purifier, so we didn’t test it.
TruSens, a new air-purifier maker that launched in early 2019, made a splash in earning a RedDot Design Award. But only the largest model, the Z3000, is true HEPA; the smaller Z1000 and Z2000 are “HEPA-type,” which is to say, not true HEPA. And the company uses 2 air changes per hour to calculate its square-footage ratings, whereas we set 4 ACH as a minimum. TruSens doesn’t list its devices’ CADR ratings publicly, nor could its customer support team provide the ratings when we asked. When we found the CADR numbers in the manuals, we were alarmed. The Z2000 (the “medium room” model), which by TruSens’s claimed specs is a direct competitor to our top pick, the Coway AP-1512HH Mighty, has a CADR of 112/117/95 on dust/pollen/smoke—in every case less than half the Coway’s CADR ratings, and below those of even our top pick for small rooms, the Blueair Blue Pure 411. The Z1000, TruSens’s “small room” model, is even weaker. Both models also draw far more power than their supposed equivalents among our picks, and both cost the same or more up front. Finally, the manual for the “large room” Z3000 does not offer CADR numbers, but with a claimed ACH of 2 in a 750-square-foot space, it’s barely half as powerful as our large-space pick, the Blue Pure 211+ (3.5 ACH in 750 square feet). Yet it costs far more up front, with a price tag of $400 versus a usual $300 for that Blueair model.
On top of the above models, we looked at and dismissed multiple purifiers from the growing crowd of knockoff manufacturers. We are not challenging their claims, though we are skeptical of them. But we do place a premium on manufacturers of long standing, with a record of customer service—and these pop-up manufacturers lack both. Rather than address them individually, we turned them into a poem, as their names (and this isn’t an exhaustive list) are quite lyrical:
Sumgott, Koios, UNbeaten, Zibrone;
Renpho, Aviano, Mooka, Keenstone;
Partu, Geniani, KeenPure, Hauea;
Cisno, Airthereal, iTvanila, Secura.
2018 and earlier tests
In 2018, we tested two large-space contenders from Honeywell, the 50250-S and the HPA300. The 50250-S failed our noise tests, registering more than 50 decibels even on its lowest setting (50 decibels is our limit for what we consider “quiet”). It’s a popular purifier, with a design that has gone largely unchanged for years, but even many of its adherents acknowledge that noise is an issue. The HPA300 performed very well in our tests but was also extremely loud, topping out at 62 decibels on its highest setting and measuring 53 decibels on the higher of its two medium speeds. It’s large and visually intrusive, too, consisting of a black tower almost 2 feet tall, 18 inches deep, and 10 inches wide. And it’s fussy to maintain, with three small HEPA filters to replace and a prefilter that you have to Velcro in exactly the right place—otherwise it will prevent the cover from reattaching. This model typically costs only slightly less than our top pick for large spaces, the Blueair Blue Pure 211+, which is a more powerful, more attractive, and quieter machine.
We retested our former budget pick, the GermGuardian AC4825. The GermGuardian performed well, but it costs far more to maintain than our current budget pick, the Blueair Blue Pure 411, because of its huge energy consumption—52 watts on medium, versus the Blue Pure 411’s 3.6 watts.
A budget contender, the Levoit LV-H132 performed poorly in our tests, reducing particulates in our 200-square-foot test room by just 60% on high, in contrast to the almost 92% reduction that our small-space pick, the Blueair Blue Pure 411, achieved.
Our former runner-up, the Winix 5500-2, once again performed well in our 2018 retest. But it costs about $800 to run over the course of five years, nearly twice as much as the comparably performing top pick, the Coway AP-1512HH Mighty. We dismissed the very similar Winix 5300-2, an alternate runner-up in a previous version of this guide, for the same reason.
The Coway Airmega 300, our previous pick for large spaces, is similar in specs to the Blueair Blue Pure 211+, our current large-space pick, which typically costs about $250 less.
We tested two tower-style units in 2017, the Coway AP-1216L and the since-discontinued LG PuriCare AS401WWA1. Despite their decent-to-solid performance, we don’t recommend either one. Their small footprints (10 by 8 inches for the Coway, 11 by 11 inches for the LG) belie the fact that they’re 32 and 30 inches tall, respectively—as tall as a kitchen counter—and so they take up a huge amount of visual space. You’d never forget that you have a purifier in the room. And at about $400 up front at the time of our review, the LG in particular didn’t justify its cost.
In 2017, we also tested the Dyson Pure Hot+Cool Link HP02 for particulate performance in the lab and in our real-world New York apartment. It offers two distinct fan functions—diffuse and focused; we tested it on both functions in the lab and in the real world. John Holecek further tested the Hot+Cool Link for VOC removal in the lab, given that Dyson had implemented an upgrade of its VOC filter since our 2016 test of its predecessor. In every case the HP02 delivered disappointing performance relative to our pick. Given its high up-front cost and relatively weak performance, we can’t recommend it.
In addition to those models, we have reviewed more than 100 purifiers since 2013, testing many of them, including the following:
In our 2014 test, the Rabbit Air MinusA2 SPA-700A earned middle-of-the-road marks in performance, cost of ownership, and noise.
When we tested the Rowenta PU6020 on particulate filtration, it did not stand out. This model employs a unique formaldehyde-trapping filter, but we think people with chemical sensitivity should look to the Austin Air HealthMate HM400 for broader odor and molecular-pollution removal. This purifier is also pricey to buy and to run.
Although the Bissell air400 has specs comparable to those of the top-pick Coway, it costs over $100 more at this writing, and it has relatively few reviews on Amazon and on Bissell’s own site.
The Philips 1000 Series purifiers cost more and have similar or weaker specs compared with our Coway top pick.
The GermGuardian CDAP4500 is a small-space unit that usually costs $150—more than our pick in that category, the Blueair Blue Pure 411—mostly because it offers Wi-Fi connectivity, which isn’t useful or necessary.
The Rabbit Air BioGS 2.0 also fails the 4 ACH limit for a standard-size room and costs more than our Coway top pick.
The Honeywell HPA200 and HPA204 (black and white versions of the same machine) barely meet our 4 ACH minimum in a 350-square-foot room (with standard 8-foot ceilings), so you’d have to run them on high constantly to get the performance we expect.
The Honeywell HFD-120-Q has specs comparable to those of our budget pick but costs more.
Hamilton Beach offers no cubic-feet-per-minute or CADR numbers on its 04386A air purifier, so we dismissed it.
The Levoit LV-PUR131 has budget specs but costs twice as much as our budget pick.
The Oransi OV200 has budget specs, draws as much as 60 watts (our budget pick draws 3.6 on medium) and costs much more than our budget pick.
The QuietPure Home Air Purifier offers specs similar to those of our also-great pick for large rooms, the Blueair Blue Pure 211+, but it typically costs more.
A budget model, the popular Pure Enrichment PureZone 3-in-1 barely met our 4 ACH minimum for small spaces.
The GermGuardian AC4100 “desktop” air purifier doesn’t meet our 4 ACH minimum for small spaces.
How to set up, use, and maintain your air purifier
To get the most out of an air purifier, you need to set it up properly, operate it properly, and perform very occasional maintenance. Here’s a list of what to do:
Remove the wrappers. Most air purifiers arrive with the filters installed—but also sealed in plastic wrappers. And we know of at least one Wirecutter reader and one Wirecutter staffer who didn’t realize they needed to remove the plastic before turning their purifier on, which rendered their purifiers useless. So open up your machine and, if the filters are indeed wrapped, unwrap and reinstall them. The HEPA filters should have an arrow or other marking indicating the correct orientation.
Place them correctly. Install your purifier at least 18 inches from a wall and any furniture, ideally near the midpoint of the room you’re using it in.
One purifier per room is best. Purifiers work best in a contiguous space; if you want to clean the air in both the living room and a bedroom, for example, it’s best to get a purifier for each room or to move a single purifier around with you. However, that’s not always practical, which is why we gave points to lightweight purifiers with handles that made moving them from room to room easy.
Oversized is better than undersized. It’s better to have “too much purifier” than not enough. Manufacturers typically base their room-size recommendations on tests with the machines set on high—no doubt for marketing purposes, but also because CADR ratings are usually based on this setting. But high is typically too loud to watch TV or sleep with. Purifiers rated for spaces larger than the one you plan to use them in can operate on lower, quieter speeds.
Keep your purifier running. Under typical conditions, we recommend running air purifiers 24/7 on their highest “quiet” setting—which we define as 50 decibels (dBA) or less. That generally means the medium setting on three-speed purifiers, or the high-medium setting on four-speed machines. Specifically, that means avoiding the “automatic” setting that some purifiers come with. We recommend avoiding this feature for two reasons. First, there’s no way of telling whether the sensor these machines use to determine their automatic on/off cycles is working properly. Second, depending on what a manufacturer determines as “poor enough” air quality, an automatic setting may let the air in your home get quite laden with particulates before kicking the purifier on.
Under known bad-air conditions, such as during a nearby wildfire, we recommend running purifiers on high for an hour and thereafter on “quiet”/medium. In 2018, we specifically tested this advice, and our results bear it out.
Keep doors and windows closed. You should keep the doors and windows closed when using an air purifier. A draft or an open door can draw unfiltered air into a room faster than the purifier can deal with it. Normal in-and-out foot traffic isn’t an issue; just close the door behind you.
Clean the prefilter monthly. For optimal performance, vacuum, wipe down, or rinse off the prefilter (it looks like a window screen or plastic netting) every month or so. The prefilter catches larger particles, such as pet hair, and keeping it clean helps the HEPA filter work unimpeded on fine particles.
Schedule filter replacement. It’s easy to forget the occasional obligation of replacing your purifier’s filters—set a calendar reminder. Purifier manufacturers typically recommend annual replacement, but check the manual to be certain; some call for less-frequent (or, rarely, more-frequent) replacement. We think it’s wisest to follow the manufacturer’s recommendation, but we have also found that HEPA filters continue to perform almost like new even after a year of continuous use—so if you blow past the deadline, it’s likely not a crisis.
What to look forward to
When we get back to our office/test space, likely late this summer, we’ll be testing the new Blue Pure 411+ (a slightly upgraded version of the former budget pick Blue Pure 411) and at least one machine from Elechomes, which is pushing enthusiastically into the air purifier category.
Frequently asked questions
What do air purifiers do?
Air purifiers of the kind we recommend use physical filters to trap small particles in your home’s air. They can capture virtually all airborne mold and fungal spores, smoke, pollen, dust, bacteria, and viruses. Many employ a second filter, containing adsorbent compounds like activated carbon, to capture gases and odors (volatile organic compounds, or VOCs)—but we have not found these to be very effective. Read more in What can an air purifier do for you?
What does HEPA mean?
HEPA stands for high-efficiency particulate air and refers to the fact that HEPA filters let air pass through with little resistance while quickly capturing almost all the particles the air is carrying. The technology was developed during World War II and designed to trap radioactive and other dangerous particles in the labs developing the atomic bomb. Read more in How HEPA filters work.
Are all your picks true HEPA purifiers?
Almost all of them are certified to the North American HEPA standard, unofficially known as “true HEPA,” which requires purifiers to capture at least 99.97% of particles 0.3 micron in diameter in a single pass. (For reference, a human hair can range from about 20 to 180 microns in diameter.) The Blue Pure 211+ is not true HEPA, but it has undergone CADR testing, which in some ways is a more rigorous standard. It has delivered exceptional air purification at the 0.3 micron HEPA standard in our testing. Read more in How we picked.
Can HEPA or H13 purifiers capture viruses, including the coronavirus?
This remains an open question. Read more in “Can HEPA Air Purifiers Capture the Coronavirus?”
How does Wirecutter pick the purifiers it tests?
We look at a range of factors, but the most important are true HEPA and/or CADR ratings, and capability based on air changes per hour, or ACH. We calculate a standardized ACH for each machine in hypothetical rooms of 150, 350, and 500 square feet. (We do this because manufacturers often give inflated claims about the size of room their purifiers will work in.) We set a minimum target of 4 ACH: Machines that don’t meet this number for a given room size are likely to have trouble keeping the air clean, especially in times of high pollution, such as during wildfires. This helps us narrow down the very large list of available purifiers to those that show particular promise. Read more in How we picked.
How do you test purifiers?
We test purifiers in real-world conditions, using guide author Tim Heffernan’s New York bedroom and spaces in our New York and Los Angeles offices. To create dirty air we burn wooden matches, which produce millions of particles in the 0.3-micron HEPA test-standard range. Then we use a professional particle counter to directly measure how well the purifiers remove the smoke from the air. And we measure the purifiers’ noise output and power consumption on their various settings, to gauge their liveability and running costs. Read more in How we tested.
I own a different purifier from the ones you recommend. Have you tested it?
Since 2013, we have tested more than 30 purifiers and dismissed many more based on their specs. To see if we’ve tested and/or dismissed yours and to read a brief summary of our findings, see The competition.
Have you tested Molekule purifiers?
Yes, we have tested the Molekule Air (the flagship model) and the Molekule Air Mini. We have a separate section about them called The worst air purifiers we’ve ever tested.
About your guide
Tim Heffernan is a senior staff writer at Wirecutter and a former writer-editor for The Atlantic, Esquire, and others. He has anchored our unequaled coverage of air purifiers and water filters since 2015. In 2018, he established Wirecutter’s ongoing collaboration with The New York Times’s Smarter Living. When he’s not here, he’s on his bike.