The Best Air Purifier

Since 2017, I have conducted extensive reporting on and real-world testing of air purifiers in my New York City apartment and in Wirecutter’s New York and Los Angeles offices. I have spoken with manufacturers, engineers, academics, and experts. And I have also lived with most of our picks, running them 24/7 for months—and sometimes years—in my apartment.

That experience has helped me gather objective data on their long-term purifying performance and any mechanical degradation. It has also helped me 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 incorrectly, can turn what should be a nearly set-it-and-forget-it appliance into a daily annoyance.

If you suffer from allergies or simply have concerns about the air quality in your home, a HEPA air purifier can help. These devices do just one thing, but they do it very well: remove fine particles from the air. They rapidly and permanently capture most common airborne allergens, including dust and pollen; mold, mildew, and fungal spores; pet dander; and dust mites and their excrement. They’re also excellent at reducing smoke from wildfires, tobacco, and marijuana. They also capture airborne pathogens—bacteria as well as most, if not all, viruses, including the coronavirus. These machines are pretty easy to live with, but for the full story, read this piece on How to Set Up an Air Purifier.

Once particulate matter settles on floors or other surfaces, an air purifier won’t lift it up. To clean allergens like pet hair and pollen from surfaces, you need a vacuum cleaner or a dust mop. To reduce viruses and bacteria on surfaces, it is usually sufficient to clean them with soap, detergent, or an all-purpose cleaner.

Air purifiers generally fall into three categories: those designed for small spaces (such as kids’ bedrooms, dorm rooms, and offices), those intended for general living spaces (such as enclosed living rooms and master bedrooms), and those designed for large spaces (including combined living/dining rooms and areas with cathedral ceilings).

The problem is that many manufacturers dramatically overstate their machines’ abilities. A lot of “living room” purifiers are barely powerful enough to keep a walk-in closet clear.

We begin by calculating projected airflow abilities. When considering a new purifier, we first refer to manufacturer-supplied specs on airflow (usually given as a clean air delivery rate, or CADR). We compute the air changes per hour, or ACH, they can provide in hypothetical rooms of 150, 350, and 500 square feet (assuming an 8-foot ceiling height).

We set four ACH as the minimum for a purifier to be considered adequate for each room size. Based on our years of real-world testing, we know that four ACH ensures rapid and nearly complete cleaning of highly polluted air.

We usually choose purifiers with true HEPA filters. 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. For reference, human hair usually measures between 20 and 180 microns across. A particle with a 0.3-micron diameter is the toughest size to remove via physical, HEPA-type filtration. So both larger and—counterintuitively—smaller particles are captured more efficiently.

The European true HEPA equivalent—which is increasingly marketed in North America as “medical grade”—is designated H13, and its requirements are virtually identical: 99.95% single-pass capture of the most penetrating particle size (or MPPS). This is typically close to 0.3 micron.

We weigh the value a purifier offers. Without setting a strict price limit within each room-size category, we compare cost against specs (especially ACH), the estimated upkeep and electricity costs over the course of five years of operation, ratings from owners, and manufacturers’ histories of reliability and customer service.

And we appreciate smart control capability. Our years of testing have proved that a good air purifier creates and maintains excellent air quality when it is simply allowed to run continuously on a moderate setting. As a result, we do not insist that our picks have smart control options.  But many members of our paid tester program have told us how helpful the ability to control appliances via an app or by voice command is for people with mobility or dexterity issues. Smart air purifiers also typically offer real-time and trend data on indoor air quality, and many allow you to set operation schedules, so that (for example) your purifier can automatically do a deep clean of your living space in the hour before you get home. In short, smart capability isn’t necessary to get clean air, but it can add meaningful utility to a purifier.

No thanks, ionizers and ozone. Many purifiers have an ionizer in addition to a HEPA filter, but most let you toggle the feature on or off, and we recommend the latter. One reason: The ionizers’ efficacy is unclear. The more important reason: Ionizers can produce a tiny amount of ozone as a by-product, and ozone is harmful to breathe (PDF). That said, among our picks with an ionizing option, none exceed the ozone production limit of 0.05 parts per million when in use, as set and certified by the strict California Air Resources Board.

A handful of air purifiers rely entirely on ozone to purify the air. We dismiss them categorically.

The tools: Since 2016, we’ve conducted dozens of real-world purifier tests, measuring particle concentrations with a TSI AeroTrak 9306—a professional, high-precision particle counter commonly used to certify air quality to OSHA standards in factories and other workplaces.

The venues: We’ve tested air purifiers in homes and in apartments. Since 2020, we’ve been testing in a room at Wirecutter’s New York City headquarters. It’s a 135-square-foot office.

The tests: At the start of each test, we take a baseline reading of the ambient air quality for three minutes. We burn five wooden matches and let the smoke circulate for two minutes to raise the particulate levels in the air. We then run the purifiers for the remaining 30 minutes.

Smoke particles are right in the 0.3-micron size range—the hardest size to capture—that’s used as the HEPA test standard. If a purifier does well on smoke, it will do even better on larger particles like dust and pollen, and—somewhat paradoxically—on smaller particles like bacteria and viruses. For an explanation, see How HEPA filters work.

We place the purifiers at the midpoint of the test room (this is best practice in your room, too). The particle counter goes in the farthest corner of the room, ensuring an accurate reading of whole-room purification. The particle counter takes readings continuously, with counts totaled in one-minute increments.

We test each purifier at least twice. In a 35-minute test, we run the machine on its absolute highest setting. It’s usually noisy. In a separate test, we use the highest setting the machine can run while keeping the noise below 50 decibels; this is around the upper limit of what would be tolerable for normal conversation, watching TV, or sleeping.

We normalize the test data so that each machine’s peak reading of 0.3-micron particles represents the maximum particulate load it faced. We describe its overall performance as its maximum reduction of particulates relative to that load. We believe this approach gives the best apples-to-apples comparison because it eliminates inconsistencies in absolute particle concentration—which even in lab conditions is difficult to reproduce exactly from test to test—in favor of a common measure.

We test new and old machines. When retesting our existing air-purifier picks, we take four measurements—two using the old filters and two using new filters—to learn how (or even if) their performance changed over time.

We also make subjective evaluations. We have always judged purifiers not just by how well they perform but also by how easy it will be to live with them in your bedroom, living room, or office. For those factors, we measure how much noise the purifiers make when running, and we calculate their long-term costs for energy consumption and replacement filters. We consider the ease of operation and maintenance, the presence or absence of distracting lights (which can disrupt sleep), the simplicity of the controls, and their physical size and aesthetics.

And we simply live with them. We station our picks in multiple homes, often for years at a time, to judge how they perform in different environments, how durable they are against rowdy kids and other sources of damage, and whether positive attributes (or persistent annoyances) are revealed as time goes by.

After over 20 rounds of testing, encompassing more than 50 different air purifiers, and after years of living with our various picks at home, the Coway Airmega AP-1512HH Mighty remains our pick as the best air purifier for most people. It has kept its place since 2015 for many reasons.

It’s a stellar performer. Across repeated testing and re-testing, the Coway Mighty has delivered some of the best performances of any purifier we’ve seen, and it has done so with amazing consistency. On its high setting, it averages more than 99% removal of smoke in 30 minutes. On medium, it averages 88%. And it maintains that performance for the entire lifespan of its HEPA filter, which should be replaced annually. We’ve always run our test units 24/7 for at least a year—in one case, for two years—and then retested them using the old filters and compared them with brand-new ones. In every case, there’s been virtually no drop-off in performance for this purifier. (Occasionally, we’ve even seen a tiny improvement: HEPA filters actually get more efficient at capturing particles as they clog up, at the expense of a small drop in airflow.)

It abides. Our first test unit ran for two years straight and was performing like new when it was discontinued for a newer version. The second one ran for four years straight, and it too was still working flawlessly when it was replaced (again due to design updates). That third model ran at our office for over two years straight while it was closed for the pandemic, during which time the office endured a small flood. The purifier was still working fine when we reopened.

It’s virtually set-and-forget. The Mighty requires very little setup and upkeep. Remove the plastic bag the filters come in, stick the filters back in the machine, and you’re ready to go. We recommend keeping the machine on the medium setting, which is quiet, energy-efficient, and effective: In past tests, we confirmed that in a room with windows and doors closed, this purifier will drop particulate levels to nearly zero within an hour and maintain that indefinitely.

It’s quiet. For a purifier of its capabilities, the Mighty is notably quiet. On medium (the speed we recommend you run it on), it measures just 39 decibels from a distance of 6 feet—a soft, fan-like whisper that’s easy to sleep or watch TV near. (Another argument for keeping it on medium is that its auto setting can rev up the fan to its highest—and much louder—speed without warning; this is true of all purifiers with an auto function.)

It goes dark. The Mighty has a feature that we’d like to see on all air purifiers: You can completely shut off its display while keeping it on the fan speed of your choosing. Purifier displays in general are overly bright, especially their air-quality indicator lamps, and if you’re sensitive to light when you’re trying to sleep, that’s a real aggravation. Many do now offer a sleep mode that (mostly) shuts off the display.

It stands up to punishment. Parents on our staff who own a Mighty report that it has stood up to toddlers banging on the control panel and older kids roughhousing with it. Senior editor Harry Sawyers said his boys discovered that it’s fun to throw balloons into the airflow (they can get stuck and hover midair) and to use it to inflate their T-shirts so they look like the Stay Puft Marshmallow Man.

It excels in air-quality emergencies, like wildfires. In 2017, we created wildfire conditions in our Los Angeles office and tested several purifiers. Using bunches of incense sticks, we created a thick haze of smoke in the room—which was four times larger than what the Coway is designed to be used in. It still dropped the pollution by 70% in under an hour, performing as well as some purifiers intended for extra-large spaces.

Operating costs are low. Running costs for the Mighty are easily the lowest we’ve found for a purifier of its abilities. Filter replacement is an annual task, whereas some competitors work on six- or eight-month cycles. And it’s energy-efficient: On the medium setting, it draws just 8.1 watts, so running it 24/7 on that setting consumes just 71 kilowatts annually. If you want to calculate that consumption as a dollar amount, the US Energy Information Administration lists up-to-date electricity rates by state.

Flaws but not dealbreakers

Some units had fan issues (but they seem to be resolved). In early fall 2020, a few reader comments and reviews showed up mentioning an imbalanced fan in the machine, which caused the whole unit to shake uncontrollably and, in some cases, led the fan to break. We asked Coway about this problem, and a spokesperson replied that Coway was aware of the issue and was working on strengthening the fans’ balancing mechanism. As of late 2022, the issue seems to be resolved, based on recent customer reviews.

Filter odors noted (also resolved). Around the same time, we saw complaints of a plasticky odor in new replacement filters. When asked for an explanation in February 2021, Coway representatives wrote: “The filter is manufactured by processing various polymer materials … and similar to new clothes, some initial odors may linger.” The reps added that the company “is currently considering adding an Air Blow process into production to minimize any potential smell and odors.”

Two Coway filters that we purchased in February 2021 had a slight odor, and filters that arrived new in 2022 had no noticeable odor at all. Most recent (2023) Amazon reviews that mention odor describe it as faint and dissipating within a day or two.

We tested two popular third-party replacement-filter sets for the Mighty, made by Cabiclean and Durabasics, and neither gave off any noticeable odor. They performed almost identically to the genuine Coway filter in our smoke tests, so we’re confident in recommending them. One caveat: Coway told us that “if a problem is identified using a third-party filter, the customer does not receive warranty service.”

The smart version technically works, but the app is lousy. We tested the smart version of the Coway Airmega AP-1512HH Mighty, the AP-1512HHS. The app is basic and buggy, but when it’s working, it does allow you to monitor and control your machine remotely. In evaluating the app, Thorin Klosowski, then Wirecutter’s editor of privacy and security coverage, found that it has terrible customer reviews, “and asked for several unnecessary permissions we weren’t comfortable granting, including access to location, the camera, and more.”

The Coway Airmega 200M is virtually identical to our top pick, the Coway Airmega AP-1512HH Mighty. The units are made by the same company, and they are physically so similar that their faceplates and filters are interchangeable. The 200M has a slightly more powerful motor, which may account for its marginally better performance in our tests: Running on its highest setting for half an hour, 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. So if you prefer the looks of the 200M, or you find it for a lower price, you can buy with confidence.

The 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 the 200M much more conducive to bedroom use. Visually, the 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.

The venerable Winix 5500-2 performed just as well as the Coway Mighty in our testing. Both machines are similarly quiet, and the 5500-2 often sells for a bit less than the Mighty. It’s not our top pick for several reasons: It’s larger and (to most eyes) not as attractive; it lacks a display-shutoff feature, except when it’s on its lowest fan setting; and it draws more electricity, contributing to slightly higher running costs. But, simply put, the 5500-2 is an impressive purifier, and several Wirecutter staffers have happily owned this model for years.

In fact, all of the Winix purifiers we’ve tested have been impressive. If you can’t find the 5500-2, the Winix 5300-2 is identical in all important respects, though it lacks the remote control the 5500-2 comes with. The same goes for the Winix C535; this one is available only from Walmart and directly from Winix, but it often sells for less than the 5500-2 and comes with a two-year supply of filters. Finally, the AM80 and the Wi-Fi–enabled AM90 are standout performers, and they offer a sleeker, more-modern look.

The Blueair Blue Pure 311i Max is another stellar air purifier comparable in capabilities to our Coway picks. It’s extremely energy efficient, drawing just 30 watts on its highest setting (out of four), versus the Coway Mighty’s 68. And it’s a fantastic performer, reducing smoke levels by 99.9% on high and 99.7% on medium-high. It’s also notably quiet. It never breaks the 50-decibel limit we consider the maximum for sleeping, conversing, or watching TV near. And it emits 39 decibels or less—to the point of being almost inaudible—on medium, low, and the ultra-low “nighttime” setting.

Blueair explained in an interview that these attributes are the result of several engineering updates working in concert. The 311i Max’s motor and fan blade are more efficient than in earlier models, with a gently flared shape and a slightly larger surface area than in its predecessor (and former pick), the 311 Auto. In the 311i Max version, a redesigned outlet grille has more area for air to pass through. The filter itself uses the same technology as all Blueair purifiers, combining a non-HEPA (but very efficient) filter with a system that imparts an electrical charge to any particles that pass through, helping them stick to the filter the next time around, essentially via static cling.

Finally, the 311i Max has an updated livability feature that was long missing from the Blue Pure lineup: You can shut off the entire control panel display and the air-quality indicator, while still keeping the fan on the speed setting you want. And its child-lock feature, also new, is helpful in households with little ones.

The filters have a shorter replacement cycle than those of the Mighty and many of our other picks, at six to nine months, depending on usage (versus, typically, a year). The machine measures actual filter usage, not simply the elapsed time since the last filter was installed, so if you don’t run your machine all the time, you’ll get more life out of filters. In the long term, though, filter replacements will likely give the 311i Max slightly higher running costs.

The Levoit Vital 200S is another excellent purifier and is similar to the Coway Mighty in both capability and livability. It excelled in our smoke tests, and it resembles the Mighty in energy usage and noise output (meaning it’s highly efficient and very quiet on its lower, everyday fan settings). There are four fan speeds to choose from (versus the Mighty’s three), so it offers a bit more flexibility. However, the medium-high setting approaches our 50-decibel limit on acceptable noise, so it’s not clear that this is a meaningful advantage.

Most important, the Vital 200S has a display shutoff that’s independent of the fan settings, so you can darken it at night while still keeping your air well cleaned. And our long-term test unit is performing without any issues, making us confident in its durability.

If you need to purify the air in a space of 500 square feet or so, we recommend the Blueair Blue Pure 211i Max. It’s extremely powerful, and in fact capable of delivering our recommended four ACH (air changes per hour) in spaces as large as 750 square feet on its highest setting (though you probably wouldn’t want to run it that way all the time).

It’s also an exceptional performer, dropping the smoke levels in our test space by more than 99.9% on its high and medium-high settings. And it’s easy to live with: quiet, attractive, and energy efficient, with a full display shutoff as well as both manual and smart controls. The relatively high price is backed up by the performance, but this much purifier is overkill for medium-size and small rooms.

The 211i Max is a thrifty operator, drawing just 41 watts on its highest setting, and 18 and 11 respectively on the medium-high and medium-low settings where you’re more likely to run it during normal use. Like the smaller 311i Max, its engineering has been updated with a redesigned motor and fan blade. Relative to its predecessor (and former pick), the Blueair 211+, the 211i Max also has a more porous outlet grille and a slightly flared design with a larger, less dense filter.

The 211i Max’s filters have a shorter replacement cycle than many of our other picks, at six to nine months (versus a typical year). The replacement alert on the display reflects actual usage, though, not simply the elapsed time since the last replacement, so if your purification demands are low, you’ll wind up on the long end of that range.

One standout test finding was that the 211i Max is remarkably quiet, particularly for a machine of its capability. On the high setting, it barely broke our 50-decibel limit for comfortable conversation, sleep, or TV watching. On its four lower speeds, it measured a barely noticeable 41 decibels or less.

Both the built-in control screen and the app show the real-time levels of airborne particulates in three size classes (1, 2.5, and 10 microns, roughly corresponding to smoke, dust, and pollen). This is standard info in an air quality monitor, but it’s something we’ve rarely seen integrated into a purifier. The app also lets you remotely monitor and adjust the operating settings.

You can manually dim or completely shut off the entire display when you want a dark room. You can also shut off the air quality indicator. A child lock function keeps young ones from altering the settings (or that’s the intent, anyway).

Finally, because the 211i Max is likely to be used in a living room or other public space, it’s gratifying that Blueair put some real care into its appearance and upkeep. The tweed-like cover (which also acts as a prefilter) is washable and, when the time comes, replaceable. A pretty, silvery gray one comes standard with the machine, and three other soft, natural colors are available.

Consider whether you actually need a large-space purifier, though. Despite its impressive energy efficiency, the 211i Max still consumes more power on its everyday medium-high and medium-low settings than the top-pick Coway Mighty (and the Blue Pure 311i Max, an also-great pick) on equivalent settings. If you’d be using a Blue Pure 211+ to purify a space that these smaller machines could handle, that’s wasted electricity.

For small spaces, like bedrooms, dorm rooms, and offices, the Blueair Blue Pure 511 is an inexpensive, easy-to-live-with, and effective purifier. Its small size and light weight mean it can sit on a desk or shelf (as well as on the floor), and its understated looks and automatic display-shutoff keep it from being a visual distraction.

In our tests, the 511 reduced smoke levels by 96.9% in 30 minutes on its highest speed, and by 89.6% on its medium speed. Even on its high setting it emitted just 48 decibels of fan-like white noise—quiet enough to sleep, work, or watch TV near. On its medium and low settings, it’s barely audible. A few moments after you change the fan speed, the entire display automatically goes dark, so it won’t bother you if you’re distracted by lights when trying to sleep.

Like all the purifiers in the Blue Pure lineup, the 511 is extremely energy efficient, using just 1.2, 3.5, and 13.6 watts on its low, medium, and high fan settings. The filter lasts about 6 months; a replacement cost about $20.

Weighing less than four pounds and standing just 13.5" high by 7.75" wide, the 511 can be easily moved around and fit into almost any space. For rooms under 180 square feet or so, it’s an excellent choice. But it is a very basic machine, with no smart functionality and no auto setting that self-adjusts the fan speed when the air quality changes. We’ll be evaluating the forthcoming 511i, which has those features, later in 2024.

If you specifically need to address high levels of volatile organic compounds (VOCs), we recommend the Austin Air HealthMate HM400. Like our other picks, it uses a HEPA filter to capture particulate pollutants. But it also contains a massive, 15-pound adsorbent filter (composed of activated carbon and a class of mineral called zeolites) that efficiently captures gaseous pollutants such as formaldehyde. Unlike the tiny, short-lived VOC filters found in most purifiers, the HealthMate’s can remain effective for several years.

That said, in most parts of the country, simply opening your windows every few days is an effective way to flush out any VOCs. Weigh that free and easy option against the HealthMate HM400’s many shortcomings: high upfront and replacement-filter costs, energy inefficiency, physical bulk, and noisy operation.

If you already have central HVAC, you can use it to supplement portable purifiers with whole-house filtration.

An easy method is to install MERV 13 filters in the return registers, and we have a guide to them. (MERV is a 0-to-16 efficiency rating used for HVAC filters, and MERV 13 or higher is recommended by the American Society of Heating, Refrigeration, and Air Conditioning Engineers for reducing airborne particulates like pollen, smoke, and PM2.5)

Here we’d draw your attention to a couple of other interesting options.

One is a sensor-equipped MERV 13 smart filter that can replace the generic central filter your system may already have (it’ll probably be installed at air handler). The other is a self-contained, independently powered filter unit that can add top-notch MERV 16 filtration to HVAC systems that were designed to use basic fiberglass or low-MERV pleated filters (and if your system is getting on in years, it likely was).

If you already have a MERV 13 or higher air handler filter in your HVAC system, along with a smart thermostat, one emerging option is the Woosh smart air filter system. This filter contains a Bluetooth-enabled pressure-differential sensor that monitors the filter’s usage and your HVAC system’s performance. Woosh founder Winston Mok explained in an interview how pairing the product with a smart air quality monitor or smart thermostat can change your understanding of your home’s air quality. (Woosh sells a monitor separately or bundled with a filter, or you can use your own).

The air quality monitor adjusts your air handler to continually address indoor air pollution. If the monitor detects an increase in particulate matter, it will tell the thermostat to ramp up the fan speed until the air is clear again. The monitor samples the air every 15 to 25 seconds, and in a demonstration, the air handler response was almost immediate (a single birthday candle set the monitor off). You can adjust the sensitivity of the monitor so that it will maintain the level of air quality and HVAC usage that you feel strikes the right balance.

The filters contain far more filter material than most. By using three pleats per inch (competitors typically use 1-2), Woosh filters pack more filtration into a given size of filter, which causes a lower pressure drop overall and less strain on the HVAC machinery. They’re rated MERV 13—the grade we recommend for HVAC systems for reduction of smoke, dust, and allergens.

Filter replacements are clever. Replacement filters consist only of the filter material itself, reducing waste. You install it in the permanent filter frame which contains the sensor and is expected to last five years. The sensor determines when the filter needs replacing by measuring how clogged the filter has become (versus a typical replacement schedule, which is chronological).

The filter can give early warnings of HVAC problems. This was an unexpected finding, Mok said. A Woosh customer had their AC compressor fail due to the condenser icing up; Woosh technicians later realized that they could have seen the impending failure in the sensor data if they’d known to look for it, so they added that monitoring ability to the software.

Woosh is not the only whole-house option we’re finding. If your HVAC system uses a coarse, net-like fiberglass or low-MERV pleated filter to protect the air handler, the Lennox PureAir whole-house air filter may be of interest. It’s a separate, self-powered fan-and-filter unit that can be added onto existing HVAC systems to improve air cleaning. The fact that it has its own fan means it puts minimal strain on the air handler—a concern for older systems that weren’t built with efficient filtration in mind. (The PureAir S, the smart version of the system, also syncs with smart assistants and smart thermostats to give you remote filter monitoring and control over your HVAC system.)

The PureAir’s MERV 16 filter is the highest efficiency below HEPA, and is exceptionally effective at capturing airborne particulates including dust, pollen, mold spores, bacteria, viruses, and smoke. A secondary activated-carbon filter reduces household odors and other volatile organic compounds (VOCs) like paint and adhesive fumes.

The PureAir also employs an ultraviolet (UV-C) sanitizing LED; this technology has been used for decades to deactivate airborne pathogens.

Asad Tahir, customer-centric product director at Lennox, noted that you will need sufficient room to install the PureAir equipment; its footprint is 16 x 25 x 5 inches. And you’ll need to get it professionally installed. After that, though, you can do the regular filter and UV replacements yourself.

To get the most out of an air purifier, you need to set it up correctly, 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 they are also sealed in plastic wrappers. Open up your machine, unwrap the filters, and reinstall them. The HEPA filters should have an arrow or other marking to indicate 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.

Oversized is okay. It’s better to have “too much purifier” than not enough. Manufacturers typically base their room-size recommendations (and CADR ratings) on tests with the machines set on high. But high is usually too loud when you’re watching TV or sleeping. Purifiers rated for larger spaces can operate on lower, quieter speeds.

Keep it 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. Under known bad-air conditions, such as during a nearby wildfire, we recommend running purifiers on high for an hour every so often to deep-clean the air.

Close doors and windows. 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—so set a calendar reminder. Purifier manufacturers typically recommend replacing them annually, but check the manual; some models call for less frequent or more frequent replacement.

In conditions where air quality is poor, like when your area is affected by a nearby wildfire, we recommend running air purifiers on high for an hour and thereafter running them on the quiet or medium setting to create and maintain clean air in the home. After burning 15 wooden matches (to create an initial heavy load of fine smoke particulates), we tested this method with the Coway Airmega AP-1512HH Mighty and the Airmega 400 over the course of three hours—one hour on high, followed by two on medium.

Set on high, the AP-1512HH reduced the particulate concentration by 99.9% in the first hour. With the purifier set on medium over the next two hours, the particulate load remained stable, varying no more than 0.1%. In the first hour on high, the Airmega 400 also reduced the particulate concentration by 99.9%, and thereafter the particulate load varied by no more than 0.2% on medium. In these tests, the purifiers handled normal ambient air after we raised the smoke levels at the outset.

In a separate, similar test, we fed the purifiers continuously smoky air by burning incense sticks throughout the test. This test also included the Coway AP-1512HH Mighty, compared against a former large-space pick, the Blueair Blue Pure 211+. In that test, we learned we had to run the machines on high to maintain meaningful purification. Both models achieved this, cutting the particulates by half or more in 50 minutes.

HEPA stands for “high-efficiency particulate air.” The filter 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. HEPA filtration is also fundamentally simple and cheap, which means it’s available to everyone today.

HEPA filtration is a physical process, but it’s not like what most people envision when they think of a filter: a net, or a colander, or maybe mosquito netting, where particles larger than the holes get caught and the rest passes through. Rather, in HEPA purifiers, a fan draws particles suspended in the air through a dense, felt-like filter that has billions of tiny gaps of varying size. Air passes through almost unimpeded—thus the “high-efficiency” in HEPA. But the maze-like web of fibers traps almost all of the particles, from relatively big material like pollen (10 microns or so) down to ultrafine, 0.01-micron (10 nanometers) stuff. That’s smaller than an individual virus.

The fibers in a HEPA filter capture airborne particulates in three basic ways (PDF).

Impaction: The largest of the particulates, about 0.5 micron and above, are captured via impaction: Unable to change their course due to momentum, the particulates simply slam into the fibers and stick to them.

Interception: Particles measuring 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.

Diffusion: Very fine particles measuring below 0.1 micron get bounced around randomly and are slowed by their interactions with atmospheric atoms and molecules. They eventually drift or get bounced into a filter fiber, whereupon (yet again) they stick in a process called diffusion.

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. According to the US HEPA standard, “most of them” means 99.97% of them in a single pass.

In 2019, we purchased a Molekule Air—the company’s iconic original purifier—and found it to be the worst air purifier we’ve ever tested. Its performance on particulate pollution was dismal—and absolutely unacceptable for an $800 device. We later learned that many of the company’s advertising claims were found to be baseless, and Molekule subsequently retracted almost all of them. (You can read about the saga in our reports from February and June 2020; the Air was then known as the MH1.) That year we also tested a Molekule Air Mini and judged it to be similarly poor.

But both of those models have been retired, so in January 2023 we purchased and tested the company’s current models, the Molekule Air Pro and the Molekule Air Mini+. In addition to a HEPA filter, the Air Pro and the Mini+ employ the company’s patented PECO technology, which Molekule claims not only captures pollutants like smoke, bacteria, and viruses—as HEPA filters do—but also destroys them using a UV-based reaction.

Molekule Air Pro: Loud, expensive, but (technically) effective

The Air Pro is Molekule’s larger purifier. Molekule’s specs claim it is effective in spaces as large as 1,000 square feet. In our testing, it did do something the original Air didn’t: effectively remove fine particles from the atmosphere. On its highest setting, it dropped the smoke levels by 99.9% in 30 minutes—as good a performance as any purifier we’ve tested. Molekule does not share the actual numbers, but presuming the claimed “3x” airflow refers to the original Air’s 90 cubic feet per minute, the Air Pro’s maximum airflow rate would be about 270 cfm, slightly higher than that of the top-pick Coway AP-1512HH Mighty.

But there’s a deal-breaking caveat. On that setting, the Air Pro emitted an earsplitting 71 decibels, measured from a distance of 6 feet. That’s by far the loudest of any purifier we’ve tested, and it would be absolutely unlivable in real-world use. I could hear its jet-like whine from 40 feet away, and it was on the other side of a heavy, acoustically sealed door. For reference, we set the limit of comfort at 50 decibels, and humans perceive a 10-decibel increase as roughly a doubling of loudness. So the Air Pro is effectively four times noisier than what we consider to be acceptable.

At its highest sub-50-decibel setting (which was speed three out of six), the Air Pro performed similarly to our top-pick Coway on its medium setting, removing 86.1% of the smoke particles we’d filled our test space with in 30 minutes. But it was louder, at 43 decibels, versus the Coway’s 39.

The Air Pro is a power hog, drawing 27 watts on speed three—more than three times what the Coway draws on medium. On its highest setting, we measured it at 111 watts (the Coway draws 68 on high), and Molekule actually lists a bigger number on the Air Pro’s spec sheet: 123 watts.

The many critical reviews on Molekule’s Amazon store frequently mention noise, an unpleasant smell (we didn’t notice it), difficulty connecting to Wi-Fi and the app, and cost. It typically retails for $1,000, and replacement filters are $160. If you kept up with the recommended six-month filter replacements, you’d spend $1,440 over the course of five years. Add the cost of electricity and the purchase price, and you’d spend well over $2,500 on a machine that performs no better on particulate pollution than the far less expensive purifiers we recommend.

Molekule Air Mini+: Similar weaknesses in a smaller package

The Molekule Air Mini+ is designed for small spaces, like a bedroom or home office. In our testing, it performed far worse than our pick for those scenarios, the Blueair Blue Pure 511 which costs less than $100, versus the Air Mini+’s typical $350 or more. On its medium setting (speed three, out of five), the Air Mini+ reduced smoke levels by just 58.7%, versus the 511’s 89.6%. And even on its highest setting, at which it emitted an intolerable 66 decibels, the Air Mini+ reduced the smoke only by 91%; the 511 captured 96.9% on highwhile emitting just 48 decibels—quiet enough to watch TV by.

Along with its high up-front cost, the Air Mini+ is also expensive to maintain, requiring a $90 replacement filter every six months. It’s not particularly power-hungry, unlike the Air Pro. But on its medium setting, the Air Mini+ still draws more electricity than the far-more-capable Coway Mighty (our top pick among purifiers and a machine capable of keeping the air clean in a far larger space). As with its larger sibling, we do not recommend the Molekule Air Mini+.

It’s a popular claim: If you stick a furnace/HVAC filter on a standard box fan, you can make a useful DIY air purifier. To test this, we taped a 20-by-20-inch Honeywell FPR 9 filter to a 20-inch Lasko box fan, and we ran that combo through the standard 35-minute, five-match test in the 200-square-foot New York City space, with the fan on high. And you know what? It did okay, cutting the initial particulate load by 87% over 30 minutes on medium. That’s nothing like the 99% reductions our top picks achieved on their high settings, but the results were better than one might expect.

If you try this hack, carefully seal the filter around its entire perimeter with clear, pro-strength packing tape—any gap would have let unfiltered air pass through, the same as on dedicated air purifiers. Doing all this may damage the fan’s motor, and we wouldn’t consider it to be a long-term solution for air-quality issues. But if you experience an air-quality emergency—say, regional wildfires creating a purifier supply shortage—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. It’s more important to measure the effect of a filter on the overall particulate load in the room. We measure purifier performance at a distance from the machines, outside the path of the cleaned airflow.

In addition to the following models, we have reviewed and dismissed hundreds of purifiers since 2013 based on their specs, features (or lack thereof), livability, and price. Some well-known brands that have never made our cut include Alen, Bissell, IQAir, Rabbit Air, and TruSens, generally based on their elevated up-front and running costs relative to those of our picks.

We have also removed from this list many since-discontinued models we tested.

The Blueair Blue Pure 311 Auto and 211+ are former also-great and upgrade picks. They’re excellent, and if you own one of them, there’s no need to replace them. The 311i Max and 211i Max that now hold these spots are slightly higher performing and have improved energy efficiency and liveability features, but the older models are truly excellent in their own right.

The Blueair Blue Pure 411i Max, a small-space purifier, is physically similar to but less capable than the also-great 311i Max. Given the minor difference in price, we think the 311i Max is the better buy, since it will excel in both bedroom-size rooms and large living areas. The older Blue Air 411 machines (the 411, 411 Auto, and 411+) are former small-space picks, but they are more expensive than the similarly performing current pick, the Blue Pure 511. They’re incredibly energy efficient but not as capable as our current small-space pick, the Blueair Blue Pure 511.

The Clorox Medium Room is a former budget pick. It’s an excellent performer with features we like, including a display shutoff. But the Blueair Blue Pure 511 is smaller, quieter, less expensive, and just as effective.

The Oransi Airmend Small Room (and the similar medium- and large-room models) have a clever design, resembling a compact box fax. Oransi designed them to meet the need for a small, portable purifier in cramped spaces like urban apartments. The Small Room was an excellent performer in our testing, but we think all the Airmends have a dealbreaking limitation: Lacking built-in buttons, they can only be operated via a tiny remote control. Little bigger than a domino, it is easy for even a responsible adult to misplace, and it’s an irresistible curiosity for toddlers and pets.

We tested the Coway Airmega Icon purifier in April 2020. It’s an interesting machine, straddling the line between appliance and furniture, and it incorporates a second function: It has a built-in, 20-watt wireless device charger. Though it is an excellent performer, we’ve concluded that a standalone (and far less expensive) purifier and a separate wireless charger are more practical for most homes.

The Mila air purifier became a special-case pick in 2020, as a truly smart purifier that was also a great performer. But since then, decent smart functionality has become commonplace in the purifier category. And after our long-term tester’s Mila inexplicably died, we discovered that her experience was not unique; one Reddit user experienced six failures. Mila’s response—“There are ~300 customers like you around the world that had 3+ failures. We call you our triple crowners and we wear that badge with shame”—helped convince us to pull them as a pick.

The Levoit Core 300, a former budget pick, is far less energy efficient than the current pick, the Blueair BluePure 511.

The Oransi Mod+ is an impressive purifier meant for large spaces. It’s exceptional at capturing particles—on a par with our large-space pick, the Blue Pure 211i Max—and competitively priced, but it lacks some of the livability features we value. It’s louder than the 211i Max, consumes considerably more electricity, and lacks smart capability.

The Winix 9800 is a solid purifier meant for large spaces. Basically an oversize version of our also-great pick from Winix, the 5500-2, it’s a terrific performer but lacks an important usability feature: Its display only goes dark when it’s on its lowest fan setting, so if you don’t want to sleep in the glow of multiple bright LEDs, you have to give up any meaningful overnight air cleaning.

The T810 is yet another impressive purifier from Winix, closely resembling the Blueair Blue Pure 311i Max in its form, performance, and sleep-friendly display shutoff. It’s slightly louder, however, and considerably less energy efficient.

The Dreo Macro Max S is a high-performing purifier with a major flaw: an enormous, bright air-quality indicator lamp that shuts itself off only in night mode, in which the fan is locked on its lowest, least effective setting. The lamp can be shut off at other fan speeds via the app, but, as with virtually all smart purifier apps, this one has many reports of connectivity issues. A manual shutoff option would be an improvement.

Blueair says its DustMagnet machines “powerfully attract airborne dust particles like a magnet before they settle on floors and surfaces.” But those claims refer to a certain size range of particles, from 0.5 to 3.0 micron—smaller than the human eye can see—so you’d have no way of knowing. In our testing with a professional particle counter, the Blueair DustMagnet 5440i performed no better than the much less expensive Coway Mighty.

Levoit’s Core 600S is a powerful machine designed for use in spaces up to about 700 square feet, at four air changes per hour, and it performed very well in our tests. However, on its medium-high and high speeds, it produced a persistent rattle that we could not ignore nor fix by repositioning the machine and confirming that the filter was properly seated.

The Honeywell InSight HPA5300B, a large-space model, likely performs well, but after measuring its electricity demands, we dismissed it. It’s an absolute power hog, drawing 33, 60, 94, and 117 watts on its four (low to turbo) speeds, respectively.

Honeywell’s HPA300 performed 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: a black tower that’s almost 2 feet tall, 18 inches wide, and 10 inches deep.

The Coway Airmega 150 is the first small-space machine from that company. It’s sharp-looking, with a clean rectangular form and a muted, matte finish available in several colors. But at its typical price of $190, it’s too pricey for a machine made for spaces no larger than a bedroom.

The Coway Airmega 250 is the larger, more powerful sibling of the Coway Airmega 150. It’s equally attractive,  but it’s only slightly more powerful than our top pick, the Coway Airmega AP-1512HH Mighty, yet it costs $200 more.

The Coway Airmega 240, a former pick for special cases, performs on a par with the top pick Coway Mighty and has a sleek design that our staff universally loved. But with more companies paying attention to their purifiers’ appearance, it’s no longer unique in combining form and function at a reasonable price.

The IKEA Förnuftig is neither a true-HEPA purifier nor an especially powerful purifier, period. It’s designed to capture PM2.5—particles 2.5 microns in diameter and above, in contrast with the 0.3-micron HEPA standard. That means it’s optimized for larger airborne particles, such as pollen and mold spores, rather than for very fine particulates, like wildfire smoke (as HEPA filters are). We tested the Förnuftig in a 200-square-foot room, focusing on how well it removed 3-micron particles from the air. It disappointed, removing just 85.2% of 3-micron particles in 30 minutes on high and 73.6% in 30 minutes on medium. Its performance on 0.3-micron particles was, as expected, worse: 64.5% removed on high and 53.5% on medium. Compared with other small-space purifiers we’ve tested in the same space, that’s very poor.

We tested the tower-style Coway AP-1216L in 2017. Despite its decent-to-solid performance, we don’t recommend it. The small footprint of 10 by 8 inches belies the fact that it’s 32 inches tall—the height of a kitchen counter—and so it takes up a huge amount of visual space. You’d never forget that you have a purifier in the room.

The AirSoap uses washable, electrically charged plates to capture airborne particulates. Our top pick Coway Mighty performed far better in our tests. AirSoap’s claim that it will save you “thousands” in the cost of replacement filters is ridiculous—you’d have to replace the filter on the Coway Mighty 20 times to reach even $1,000, which means you’d have to run it for two decades.

The Aeris Aair 3-in-1 Pro performs similarly on particulates to our pick for large spaces, the Blueair Blue Pure 211i Max, and it contains a large VOC filter composed of 2.2 pounds of activated carbon and alumina, which should make it far better at capturing VOCs. But it’s expensive, the filters last only six months, and replacements cost about $200.

AirDoctor sells an expensive purifier with a filter that it markets as “UltraHEPA,” claiming that the filter traps particles 100 times smaller than what HEPA filters can capture. It’s not true: All true-HEPA filters snag virtually 100% of the nanometer-scale particles that AirDoctor says is its unique ability to capture.

We’ve tested many Dyson purifiers over the years, most recently (2019) the Pure Cool TP04 and Pure Hot+Cool HP04. Neither model measured up well against our top pick, the Coway Mighty. We have also found no evidence that the fan function on Dyson purifiers 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 deliver filtered air rapidly into the farthest corner of a room.

The Medify MA-40 performs similarly to the top-pick Coway AP-1512HH Mighty, but it’s much  louder, at 52 decibels (above our 50-decibel definition of “quiet”) on its medium setting and 42 on low. The Coway measured 39 decibels and 31 decibels (nearly inaudible), respectively.

The huge and exceptionally powerful Medify 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). But at 28 inches tall and 15 inches wide, it’s best suited to large commercial or public spaces—like casinos, which Medify says use the MA-112 to counter the effects of cigarette smoke.

The GermGuardian AC5900WCA was a star performer in our 2019 test, but we also found it to be much louder than the top-pick Coway Mighty, measuring 47 decibels versus 39, on its quiet/medium setting. And the quality of the sound was rough and whooshy, versus the Mighty’s steady white noise. It’s far more expensive to maintain, as well.

The Levoit LV-H133 is another competitor to the Coway Mighty. But it’s more expensive up-front as well as over the course of five years of 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 in its CADR specs than our small-space pick, the Blueair BluePure 511.

A budget pick contender, the Levoit LV-H132 performed poorly in our tests, reducing particulates in our 200-square-foot test room by just 60% on high.

Our previous top picks among large-space purifiers, the Coway Airmega 400 and Coway Airmega 300, are impressive performers. The same is true of the Coway Airmega 400S, a smart version of the 400. But the Blue Pure 211i Max, our equally capable current pick, comes out on top on price: It typically sells for several hundred dollars less.

Winix’s HR900 Ultimate Pet Air Purifier has lower specs than our less expensive top pick from Coway.

The Hathaspace Smart True HEPA Air Purifier has solid reviews and typically costs a bit less than the top-pick Coway Mighty. For that price, though, you get a machine that’s barely a third as capable: The Hathaspace purifier can produce, at most, two air changes per hour in a 350-square-foot room, whereas the Mighty purifier can deliver 5.7.

The GermGuardian AC4825 has been around for years and is, up front, cheap. But because of its higher energy consumption, it costs more to maintain than many more-capable purifiers, and it’s a tall, garish device that won’t blend into any decor outside of an Alien set.

In addition to the above models, we looked at and dismissed multiple purifiers from the growing crowd of knockoff brands. It’s plainly a Duff Dry situation, and there’s no reason to doubt that these suspiciously similar knockoffs would perform all that differently from the originals. But we place a premium on long-standing companies with a record of customer service—and these pop-up brands lack both attributes. Rather than address them individually, we turned them into a poem, since their names (and this isn’t an exhaustive list) are quite lyrical:

Sumgott, Koios, UNbeaten, Zibrone;

Afloia, Aviano, Mooka, Keenstone;

Partu, Geniani, KeenPure, Hauea;

Cisno, Druiap, iTvanila, Secura.

This article was edited by Harry Sawyers.