The Auto designation in the name indicates that, unlike previous generations of Blue Pure purifiers, this model contains a particle sensor. That feature allows you to set the machine to an automatic mode, in which it adjusts its speed depending on the air quality in the room. You can also set it manually to its low, medium, or high fan setting.

We like that the Blue Pure 311 Auto automatically shuts off the white LED lights on its control panel, on top of the unit, after a few moments. Like the Winix models, however, it shuts off its bright blue air-quality indicator lamp only when you’ve manually set it to low. In a dark room, the lamp can be a distraction, and we wish this model offered an option to shut it off on every setting, as you can on the Coway AP-1512HH.

Blueair recommends replacing the filter “every six months or so.” Following that schedule, you spend $80 a year on replacements versus about $50 or less for the Coway AP-1512HH and the Winix machines. And though we’ve run the filters 24/7 on another Blueair machine, the Blue Pure 211+, for up to a year and found no meaningful degradation in performance, when we retested the 311 Auto on year-old filters, it dropped from 94% to 86% removal of smoke on its medium setting. That’s still solid, and when we installed new filters and tested again, the machine performed like new—the motor and fan were working perfectly. But we take that result as an indication that the 311 Auto is a more sensitive to filter life than some other purifiers, so it’s best to stick to the six-months-or-so schedule.

How the Blueair Blue Pure 311 Auto has held up

A compact purifier similar in performance to the Coway Airmega AP-1512HH Mighty and our other also-great picks, the Levoit Core 400S adds voice control via Amazon Alexa or Google Assistant, along with remote manual control through an app. Although most people are likely to be well served by purely manual or basic automatic purifiers (those that have a built-in air-quality sensor and adjust to changing conditions), if you are an avid smart-home proponent, or if mobility, dexterity, vision, or other issues make it difficult for you to adjust appliances, the Core 400S is a highly capable and relatively affordable option.

With a clean air delivery rate (CADR) of 260 cubic feet per minute on high, the Core 400S is slightly more powerful than our top pick, the Coway AP-1512HH, which has a CADR of 240. In practice, that doesn’t make much difference, and indeed the Core 400S delivered numbers almost identical to those of the AP-1512HH in our testing, reducing 0.3-micron smoke particles by 99.1% in 30 minutes on high. The Core 400S has four speed settings versus the AP-1512HH’s three, and on its “third gear”—which, at 46 decibels, is the highest sub-50-decibel setting that we consider quiet enough for conversation or TV watching—it outperformed the AP-1512HH, removing 96.3% of smoke particles in 30 minutes, versus 87.7% for the Coway model. But it also draws twice the electricity (16.1 watts versus 8.1 watts) and moves more air per minute on that setting than the AP-1512HH does on its medium speed, so that’s not surprising. The AP-1512HH, meanwhile, generates just 39 decibels of noise on medium; on top of that, we know from testing that the AP-1512HH creates and maintains extraordinarily clean air when run continuously on medium, as we recommend for all purifiers. In short, we don’t consider the Core 400S’s 30-minute superiority to be a meaningful advantage.

Where the Core 400S stands out is in its smart functionality. You can manually remote-control it via Levoit’s VeSync app, and through the app you can also sync it with Amazon Alexa and Google Assistant, enabling voice control. If you’ve already shifted your home to one of those systems, this air purifier should be a seamless addition: In our tests on an Android phone, installing the app and connecting the Core 400S was easy. If voice control will help you address mobility, dexterity, vision, or other issues, that’s another good reason to consider the Core 400S.

The VeSync app provides basic but useful controls: You can set timers, adjust the fan settings, program the machine for optimal operation in different-size rooms, turn the machine and its display on and off, and monitor the air quality—although in testing, we found its AQI (air-quality index) reading to be consistently lower than the local EPA readings as reported in the AirNow app, one of our recommendations for air-quality monitoring. (For this test, Tim placed the Core 400S on his balcony, which is about a mile from the closest official outdoor monitoring station.)

Thorin Klosowski, Wirecutter’s editor of privacy and security coverage, is somewhat critical of the VeSync app: “There are plenty of customer reviews complaining about the potential personal-data issues. The VeSync app (named for the parent company of Levoit) is designed to work with products from several other brands, such as Etekcity and Cosori, and also serves as an online store as well as a customer-service hub. The company’s sprawling privacy practices cover devices ranging from smart scales to foot massagers, which makes its policies even more difficult to parse, let alone verify. Suffice to say, we were not pleased to learn that VeSync had automatically signed us up to receive email marketing that we never explicitly agreed to [when testing a Levoit smart humidifier]. We were heartened to learn that the company, in 2021, instituted a bug bounty program, which allows security researchers to report bugs they find for cash rewards. The program is still new, but we’ll keep an eye on how the company reacts to submitted bugs.” If you’d rather avoid any privacy concerns, the Core 400S also allows for manual control—no need to use the VeSync app at all.

The Levoit Core 400S is not our top pick for a few reasons. Up front, it’s usually a bit more expensive than the Coway Airmega AP-1512HH Mighty and the Winix models we recommend, and its greater power draw on its highest “quiet” setting may add a bit to running costs over time. That noted, it’s a compact (11 inches wide by 20 inches high) and reasonably attractive machine with highly positive owner reviews and an established company behind it, so long-term maintenance should not be a problem.

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 650 square feet (assuming an 8-foot ceiling). That means it can clean the combined living areas of many open-floor-plan homes. It’s also an attractive, quiet-running machine, so it’s easy to live with. Its five-year cost of ownership—about $1,150 including the up-front cost and the annual cost of electricity and replacement filters—is comparable to that of most large-space purifiers. All that said, unless you need to clean an especially large space, the even quieter, smaller, and much more affordable Coway Airmega AP-1512HH Mighty is a better choice.

In January 2021, the similar Blue Pure 211+ Auto was released. It’s slightly more powerful (not in a way that is likely to make a meaningful difference) yet also more energy efficient due to a new motor and filter, and it adds an auto setting that adjusts the fan speed to changing air-quality conditions. We have not been able to test it, but we are confident that it will deliver similar, excellent performance.

In our 2019 tests, 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, with filters that had seen eight months of 24/7 use. With new filters, it reduced particles by 99.3% and 99.2%, respectively. A year later, with those same filters—far past their recommended six-month replacement schedule—the numbers barely dropped, reaching 99.1% and 98.0%, respectively. Those results make the Blue Pure 211+ one of the most efficient air purifiers we’ve tested, as well as one of the most consistent on different settings. And the fact that it maintained its high performance even on significantly overused filters gives us confidence in its long-term performance.

The Blue Pure 211+ is not a true-HEPA purifier. 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 old filters.

It delivers 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 competitors that cost far more. On its quiet/medium setting, it delivers performance at a CADR of 231 for smoke, pollen, and dust—roughly what the Coway Airmega AP-1512HH Mighty offers on high. In a 500-square-foot space with 8-foot ceilings, that means it makes 5.3 ACH 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 an unusual mechanism to boost its performance. The machine imparts an electrical charge to any particles that initially pass through its filter. When those 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 its high and quiet/medium fan speeds. (This mechanism is distinct from the ionizers found on many purifiers, including the AP-1512HH, which 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 after living with the Blue Pure 211+ for a year, we decided it’s best for large spaces specifically. It’s physically quite a bit larger than the AP-1512HH, 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 than the Coway model, at 43 decibels 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. (The sound is 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 respective machines’ everyday, medium fan settings, the Blue Pure 211+ draws a lot more power than the AP-1512HH, consuming 46.8 watts versus 8.1 watts. That’s 1.1 kilowatt-hours a day, 33 kWh per month, or 401 kWh per year for this Blueair model versus 0.2 kWh, 6 kWh, and 73 kWh, respectively, for the Coway machine. If you’re using a Blue Pure 211+ to purify a space that the AP-1512HH can handle, that’s a lot of wasted electricity.

Compared with the other large-space purifiers we’ve tested, the Blue Pure 211+ is similar in its five-year costs. Including its typical up-front price of about $300, and a total of about $800 in electricity costs and filter replacements (which the company recommends handling every six months), it will set you back about $1,150 over that period. It’s close in overall costs to our former top pick for large spaces, the Coway Airmega 400. 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 a bit more to buy and run for five years, and it’s louder, larger, and less attractive than the Blue Pure 211+. We really like the 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.)

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 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. 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 the Core 300 outperformed considerably.

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 Core 300 reduced particulates in our 135-square-foot New York test room by 97.4% in 30 minutes. On medium, where it produced 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 Coway Airmega 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 produces much lower airflow than the AP-1512HH—a 135 CADR versus the AP-1512HH’s 240 CADR—and is not adequate for the living-room-size spaces where the AP-1512HH 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 14.5 inches tall and 8.5 inches wide, so it fits on a bedside table or the corner of a desk. On its medium and low speeds, it’s quiet enough for sleeping or conversing near (43.2 decibels on medium and 38.7 decibels 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 AP-1512HH), 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 up front, but it is not an 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 AP-1512HH draws just 8.1 watts. Running the Core 300 on medium speed 24/7, you consume about 303 kilowatt-hours per year; the filters also need to be replaced every eight months. Over the course of five years, its running costs may be as much as 1.5 times the operating costs of a machine like the AP-1512HH. That still may feel manageable on a monthly basis, and the Core 300’s low up-front purchase price is easier to swallow than most of the other options. 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.

If you’re concerned about VOCs: Austin Air HealthMate HM400

If you live in an environment with consistently 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 including VOCs such as 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, fresh paint and wood finishes, and car engines. Most of our picks have token adsorbent filters that amount 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 in this regard. 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. All that said, in most parts of the country, simply opening your windows every few days is an effective way to flush out any VOCs.

When it comes to handling 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 Airmega AP-1512HH Mighty; the dense VOC filter causes this machine to work slower and consume 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 the 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, at which the HM400 consumes 81.8 watts, it should total about three times the five-year running cost of our top pick, the Coway AP-1512HH.

If you simply need to remove particulates from your air in a large space, the Blueair 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.

If you want maximum energy efficiency in a small space: Blueair Blue Pure 411 series

The Blueair Blue Pure 411 series encompasses three similar models: the original Blue Pure 411 (a former pick for small spaces), the Blue Pure 411 Auto, and the Blue Pure 411+. Although Blueair says the latter two models are slightly more powerful, they share the same clean air delivery rate (CADR) of 120, making them appropriate for spaces up to about 180 square feet. The differences between the machines are minimal: The 411 Auto has a particle sensor and thus can run in an automatic mode, adjusting the fan speed to meet changing air-quality demands, whereas the other two are manual operation only.

In our testing, the machines did not match the rapid air cleaning of our current small-space pick, the Levoit Core 300. But they did well compared with other small-space machines we looked at, averaging about 85% removal of smoke particles in 30 minutes on high and about 65% in 30 minutes on medium in a room of 200 square feet. Over a longer timeframe—and especially if kept running on medium 24/7, as we recommend for all our purifier picks—they will create and maintain very clean air in a typical home office or bedroom.

Although these models are not our first choice because of their slower rate of cleaning, we are comfortable recommending them for their exceptional energy efficiency and correspondingly low long-term running costs. On medium, running around the clock, they consume only about $6 worth of electricity per year. Replacement filters cost $19, and if you stick to the six-month replacement schedule, they add up to just $171 (nine filters) over the course of five years. The total five-year running costs are thus just $200, about 60% less than the costs of the Levoit Core 300. Add in the Blue Pure 411 models’ quiet operation and good looks, and they are an attractive option for small spaces.

If you want a truly smart air purifier: Mila

The Mila air purifier is a notable entrant in the nascent category of truly smart air purifiers. When we tested it in October 2020, it delivered excellent performance on smoke particles, virtually identical to the performance we got from the Coway Airmega AP-1512HH Mighty. In comparison with the features of other smart air purifiers we’ve looked at, its app, sensors, and programmability are head and shoulders more advanced—almost another species. The Mila is now available on Amazon, too. Although we believe that most people are likely to be happy with a purely analog or automatic purifier (those with an air-quality sensor that adjusts the machine’s speed to changing conditions), if you’re keen on smart appliances, the Mila is worth considering.

The Mila contains multiple sensors, which measure three sizes of particulates (1, 2.5, and 10 microns), carbon monoxide, VOCs, and humidity. In our long-term testing in Tim’s home, it responded rapidly to changes in air quality—when Tim was cooking or baking and creating smoke, and when he was cleaning his bike chain with solvent, the Mila quickly increased the fan’s speed to clear the air more efficiently. On dry winter days, it reliably warned of low humidity.

You can set the machine to an automatic mode in which it monitors the air and adjusts itself, or you can control it via the Mila smartphone app, which is available for both iOS and Android. The app allows you to choose from various modes (to maintain the absolutely cleanest air possible at the expense of higher and noisier fan speed, for example, or to run a deep-cleaning cycle in the hour before you go to bed and then cycle down so that the machine runs on a quiet setting while you sleep). The air-quality readings it takes are stored and viewable in the app, so you can get a long-term picture of your home’s air quality. And the app sends alerts when something needs your attention, such as a sudden spike in particulate pollution.

Tim didn’t find those options particularly useful and largely let his test unit run in the automatic mode, but two other Wirecutter staffers who are testing the Mila in their homes (and are more tech savvy) have appreciated the ability to monitor their air quality from afar and to control the machine remotely.

When fitted with the Basic Breather filter, the Mila is capable of cleaning the air in a space of almost 500 square feet at our recommended 4 air changes per hour (ACH), as it has a robust maximum clean air delivery rate (CADR) of 263 cubic feet per minute when operating at its highest level. At that fan speed, however, it’s far too loud for anyone to make conversation or watch TV nearby. Having that power available for an emergency situation, such as a nearby wildfire, is nice, but for everyday use you would probably want to run the machine on lower speeds and in a smaller room—350 square feet or so.

The Mila works with multiple filters, some of which contain significant amounts of activated carbon for VOC removal. For particulate removal, all the filters are rated at the European HEPA standards H12 to H14. H13 corresponds to the US HEPA standard, but all are highly effective; the differences between H12 (99.6% removal of fine particles in a single pass) and H14 (99.995%) are so minor that in home usage they make virtually no difference. The higher-rated filters do restrict the airflow somewhat, however, which is why the Mila’s maker recommends them for bedrooms or small living rooms rather than large open spaces.

A purifier with a built-in wireless charger: Coway Airmega Icon

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. This model performed exceptionally well in our tests, removing 99.6% and 97.4% of smoke particles in 30 minutes on high and medium, respectively. It’s also notably quiet on its low and medium settings, where it would normally be running, putting out 33 and 43 decibels, respectively. (On high, it puts out 54 decibels, too loud for restful sleep or watching TV.) And the charger worked flawlessly on the iPhone we tested it with.

The Icon has a CADR (clean air delivery rate) of 186 on smoke, 194 on dust, and 235 on pollen, which works out to our recommended 4 ACH in a space of roughly 375 square feet when set on high, or a bit lower on our recommended (because quieter and more energy efficient) medium speed. At any rate, that makes it suitable for a large bedroom or typical living room. A second version, the IconS, features Coway’s app for monitoring and remote control, but in the past we have recommended against its other smart purifiers because of concerns over the app’s intrusive permissions requests. (These concerns have been passed on to Coway’s engineers, who have been responsive to our feedback in the past.)

Is this model worth the typical $650 price ($700 for the IconS)? That’s a matter of taste and budget, and whether you think the wireless charger adds significant value. If your main concern is air quality, you can certainly find purifiers that are just as powerful—such as the Coway Airmega AP-1512HH Mighty, the Winix AM90, and the Blueair Blue Pure 311 Auto—for far less. But we expect this sort of design-forward, multipurpose purifier to become more common as improving air quality becomes a concern in many households.

Great looks without a big price premium: Coway Airmega 240

The Coway Airmega 240 is not a special cases pick for any unique abilities; rather, the special case is that you want a terrific-looking as well as high-performing and well-priced air purifier. As purifiers become standard appliances in more and more homes, manufacturers are increasingly designing truly attractive machines, but in many cases they come at a significant cost premium over more utilitarian, and often more capable, purifiers—sometimes hundreds of dollars more. The Coway Airmega 240 addresses these issues. It is slightly more powerful than our top-pick Coway Mighty, and achieved nearly identical results to it in our smoke tests: 98.7% removal of smoke particles in 30 minutes on high, and 90.1% on medium. It also usually costs only a bit more than the Mighty( about $50). Our staff universally praised its looks in an informal survey. “Total Art Deco vibe,” said one. Two mentioned (as a high compliment) that it looks like a modern, minimalist radiator cover. If it catches your eye, know that it works as well as it looks.

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 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.

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 that this trick 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, 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 air 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.

We have long recommended 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. 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 Airmega 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.

Set on high, the AP-1512HH reduced the particulate concentration by 99.9% in the first hour. 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 starting up a 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 Airmega AP-1512HH Mighty, and our large-space pick, the Blueair Blue Pure 211+, on handling ongoing smoke from burning incense sticks. And in that test, we learned that we had to run the machines 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.

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. Happily, 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 mazelike web of fibers traps almost all the particles, from “big” stuff like pollen (10 microns or so) down to ultrafine, 10-nanometer (0.01 micron) stuff. (That’s smaller than an individual virus.)

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, the particulates simply slam into the fibers and stick to them. 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. Finally, very fine particles, namely those measuring 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 they 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.

Let’s begin by defining what the IKEA Förnuftig is not: a true-HEPA purifier, or an especially powerful purifier, period. It’s designed to capture PM2.5—particles 2.5 microns in diameter and above, in contrast to 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. (HEPA filters capture larger particles even more efficiently than very fine ones; PM2.5 filters also capture finer particles but with lower efficiency.) An IKEA representative told us that “this is a deliberate design consideration, to find the right balance between affordability, small form factor for high home furnishing appeal and low energy consumption, while retaining a comparably high air flow and CADR.” Fair enough, but with a clean air delivery rate (CADR) of just 82.4 cubic feet per minute, the Förnuftig is appropriate only for very small rooms, no more than 125 square feet (and IKEA suggests just 100 square feet, a 10-by-10-foot space). In short, it’s cheap, sleek—and weak. We don’t recommend it.

Tim tested the Förnuftig in his 200-square-foot spare room, using the methods described above. But rather than focusing on its performance on 0.3-micron particles, he noted how well it removed 3-micron particles from the air. (IKEA confirmed that this was the appropriate size to look at; it’s the closest to PM2.5 that our TSI AeroTrak particle counter can measure separately.) The Förnuftig disappointed, even when we considered that the test room was larger than the space the machine is meant for, as it removed 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 our budget/small-space pick, the Levoit Core 300, which removed 97.4% and 92.6%, respectively, of 0.3-micron particles and removed virtually all 3-micron particles on the same settings, that’s very poor.

Upon its launch, the Förnuftig was not available in California, and we noted this shortcoming. It has since received California Air Resources Board certification (meaning it emits no more than 50 parts per billion of ozone) and can be sold in and shipped to California.

Finally, although the Förnuftig has a token VOC filter, you have to purchase that piece separately; most air-purifier makers include VOC filters upon purchase and as part of their replacement-filter sets. Installing the VOC filter also lowers the machine’s CADR to just 70.6 cubic feet per minute.

The above findings make the Förnuftig an automatic dismissal under our criteria. We highlight it here only because it’s of interest to many readers.

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 in 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 those models have been retired, so in January 2023 we purchased and tested the company’s current models, the Molekule Air Pro and Moleklule Air Mini+. A separate write-up on each follows, but it’s worth noting a feature they share in common: In October 2022, Molekule released a new type of filter that they both now use. The PECO-HEPA Tri-Power filters incorporate, as the name suggests, a HEPA filter. We’re glad they do, as HEPA filtration is a thoroughly established, extraordinarily effective method of permanently removing fine particulate matter from the air, down to at least 10 nanometers. That’s below the size of bacteria and viruses, including the SARS-CoV-2 coronavirus. We’re also darkly amused by this development, given the company’s earlier, and since retracted, claim that its “scientifically-proven nanotechnology outperforms HEPA filters in every category of pollutant.”

In addition to a HEPA filter Air Pro and Mini+ employ the company’s patented PECO technology, which Molekule claims does just capture pollutants like smoke, bacteria, and viruses, as HEPA filters do, but destroys them using a UV-based reaction. For more on that, see the reports linked in the opening paragraph.

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. It’s unclear how that figure is calculated, and based on years of experience, we doubt the Air Pro is capable of producing our recommended four air changes per hour in a space that big. 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.

But there’s a dealbreaking caveat. On that setting, the Air Pro emitted a earsplitting 71 decibels, measured from a distance of six feet. That’s by far the loudest of any purifier we’ve tested, and 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 acceptable.) And frankly, this good performance was not surprising: The Air Pro moves a lot of air per minute on its highest setting, and if you draw a lot of air through a HEPA filter, virtually all particulate pollution will rapidly be captured. It’s a simple, highly effective, purely physical process—one that our picks all excel at. (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 the top-pick Coway AP-1512HH Mighty.)

At its highest sub-50-decibel setting, which was speed three of a total six, the Air Pro performed similarly to our top-pick Coway on its medium setting, removing 86.1 percent 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. That performance further bolstered our belief that the Air Pro’s HEPA filter, not its PECO technology, is doing most of the particulate removal.

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 the noise of the Air Pro. (Wrote the owner of a salon who bought one to attempt to reduce odors: “The highest setting is so loud we can not talk to our customers while it’s on high.”) An alarming number of them mention that the machine produces an unpleasant smell (one reviewer compares it to gasoline) when the purifier is first turned on. Molekule acknowledges this issue in its user manuals and suggests that the odor will dissipate within 48 hours of continuous filter use, describing smell as “safe and expected,” but some people report that the smell never disappears, even after months. (I didn’t notice a smell, but the test room was filled with smoke that may have masked other odors.) Difficulty connecting to WiFi, a buggy app, and frequent error codes also come up as complaints.

Finally, and repeatedly, so does the Air Pro’s cost—something that alone would lead us to dismiss it, even if it performed beautifully in every way. It typically retails for $1,000, and replacement filters (“average use 6 months” per the Molekule site) are $160. If you kept up with that cycle, you’d spend $1,440 on replacement filters 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 inexpensive (to buy and run) HEPA air purifiers we recommend. We do not recommend the Molekule Air Pro.

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 Levoit Core 300—which costs about $100, versus the Air Mini+’s typical $350 or more. On its medium setting (speed three, out of a total five), the Air Mini+ reduced smoke levels by just 58.7%, versus the Levoit’s 92.6%. And even on its highest setting, on which it produced an intolerable 66 decibels, the Air Mini+ only reduced the smoke by 91%; the Levoit captured 97.4% on high, while measuring at 54 decibels. That’s a bit too loud for continuous use, but less than half as loud (in terms of human perception) than the Air Mini+.

Along with its high upfront 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 it 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+.

2023 tests

The original (and now discontinued) Molekule air purifier—first known as the MH1, and later as the Air— turned in the worst performance on particulates of any purifier, of any size, of any price, that we have tested in the nearly 10 years that we have been producing this guide. The later (and also discontinued) Air Mini outperformed it, but that’s not saying much: The Mini still produced the second-worst performance we’ve ever seen. A pair of cases before the National Advertising Division and National Advertising Review Board of the Better Business Bureau backed our test results: All of Molekule’s quantified claims about the Air’s performance, all of its claims about its PECO technology’s 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 deemed unsupported. Other claims, the boards ruled, were too broad. Molekule retracted all of them. It’s sort of beating a dead horse, since neither of these machines is still being produced, but if you want more details, see our reports from February and June 2020.

2022 tests

We tested the Blueair DustMagnet 5440i, the most powerful among several Blueair DustMagnet models, which is comparable in airflow to the Blueair Blue Pure 211+, our pick for large spaces. Blueair says that the 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, and specifically do not apply to particles outside that range. When we compared the DustMagnet 5440i at that size range with one of our standard-space purifier picks, the Winix AM90, the performance differences were negligible. But their price difference isn’t—as of autumn 2022, the 5440i typically sells in the mid-$400s, more than twice the AM90’s usual price. The DustMagnet design allows the 5440i to serve double duty as a small side table, because the air blows out of the sides instead of the top as on most purifiers. That’s a nice additional use for an appliance that will sit in your living room or bedroom. But the horizontal airflow also creates a constant breeze in the room when the machine is operating, which might not be desirable.

Levoit’s Core 600S is a powerful machine designed for use in spaces up to about 700 square feet at 4 air changes per hour. And it performed very well in our tests, as you might expect when you run a large-space machine in a small room. However, on its medium-high and high speeds, it produced a persistent rattle that we could not ignore, nor could we fix the problem by repositioning the machine and making sure that the filter was properly seated.

The Winix A230, a small-space purifier suited for bedrooms or offices, performed well in our tests—seemingly too well for such a small machine. Afterward, we realized that we had inadvertently tested it with its ionizer function on, and we recommend against ionizers because of their (admittedly small) production of ozone. We’ll retest the A230 in the future with the ionizer off; if it continues to perform well, it’s a contender to join the Levoit Core 300 as a budget, small-space pick.

The Honeywell InSight HPA5300B, a large-space model, likely performs well, but after measuring its electricity demands, we dismissed it. Compared with our pick for large spaces, the Blueair Blue Pure 211+, the HPA5300B is a power hog, drawing 33, 60, 94, and 117 watts on its four (low to turbo) speeds, respectively. The Blue Pure 211+, in contrast, tops out at 64 watts on its highest setting yet is also a slightly more powerful machine in terms of clean air delivery rate (CADR). The HPA5300B also has a visually imposing presence, with its stark black color and huge size (22 inches high, 19 inches wide, and 10 inches deep, by our firsthand measurements).

2021 tests

The Coway Airmega 250 (aka the Coway AP-1720H) is the larger, more powerful sibling of the Coway Airmega 150, which we tested in 2020. It shares the Airmega 150’s clean rectangular form and elegant matte finish, and it performed very well in our tests, removing 99.4% and 95.6% of fine smoke particles on high and medium, respectively, in a 200-square-foot space. But it’s only slightly more powerful than our top pick, the Coway Airmega AP-1512HH Mighty, yet costs $200 more. For that reason, we did not make it a pick, but if you prefer its looks and don’t mind paying for them, it’s a solid performer for spaces of up to about 400 square feet. (Coway claims that it’s able to handle 930 square feet, but that’s based on 2 air changes per hour, whereas we recommend 4 ACH.)

We tested the Shark Air Purifier 6, a large-space machine; the company also had a less powerful model, the Shark Air Purifier 4. Both models are now discontinued, and we will remove them from this guide and provide an update with newer Shark models if we test the company’s purifiers again. The Air Purifier 6 performed very well, as you might expect of a machine with a stated clean air delivery rate (CADR) of 325 cubic feet per minute. But it cost $450, versus $300 for our large-space pick, the Blueair Blue Pure 211+, and the Blue Pure 211+ was more powerful, with a CADR of 350. In addition, we disliked this Shark model’s design: It was especially tall at 32 inches and quite wide at 17 inches, and it came only in black, so it had an imposing visual presence. On top of that, we worried that it could present a tipping hazard in homes with toddlers, because it was just 8.5 inches deep—a shallow footprint for something that was nearly the height of a typical kitchen counter.

2020 and 2019 tests

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; in addition to white, it comes in a pretty sage green and a soft pink. It performed quite well in our testing, capturing 98.2% and 78.5% of smoke particles in half an hour on high and medium, respectively. It’s also quiet (34 decibels) on its medium setting, on which it draws a thrifty 6.9 watts. But at a typical price of $190, it’s too expensive for a machine made for spaces no larger than a bedroom. You can get the much more powerful Winix AM90 or AM80 for about the same price, or you can choose the Winix 5500-2 or 5300-2 for less.

The AirSoap, unlike all the other purifiers we have tested, does not contain a physical filter. Instead, it uses washable, electrically charged plates to capture airborne particulates. It did reasonably well in our testing, removing 95.2% of the smoke on high and 89.7% on medium. But our top picks from Coway, Winix, and Blueair performed far better. The 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 AP-1512HH 20 times to reach even $1,000, which means you’d have to run it for two decades. And the need to frequently wash the plates—and, once a year, take the whole machine apart and give it a deep clean—sounds like a hassle rather than a selling point.

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. On top of that, the HEPA filter is 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 although the Aair tested well, it did not perform any better on particulates than our much less expensive pick for large rooms, the Blueair Blue Pure 211+. The Aair reduced particulates by 98.1% and 94.1% on high and medium, respectively, in our 30-minute tests; the Blue Pure 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 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.

In 2019, we tested two of Dyson’s latest-generation air purifiers, the Pure Cool TP04 and Pure Hot+Cool HP04. Of the two, the TP04 performed better, but neither model measured up well against our top pick, the Coway Airmega AP-1512HH Mighty, and our large-space pick, the Blueair Blue Pure 211+. The TP04 reduced particulate pollution by 86.6% in 30 minutes on its highest setting; compare that with 98.9% and 99.3% from the AP-1512HH 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 models, in contrast, 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 considering 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 did not test the Dyson Pure Hot+Cool HP06 Cryptomic purifier, but we did speak at length with a Dyson engineer and representative about it. In particle filtration, it is virtually identical to the Pure Hot+Cool HP04 (see the paragraph above), as it uses the same HEPA filter and produces only marginally lower airflow. We would not recommend it for the same reasons we do not recommend the HP04. The HP06 adds a molecular formaldehyde filter, which Dyson calls Cryptomic technology. (We have also not tried Dyson’s newer version of this model, the HP07.)

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, and in our tests 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 decibels on low. For comparison, the AP-1512HH measured 39 decibels on medium and 31 decibels (nearly inaudible) on low. Typically, this Medify model also costs more than that Coway purifier.

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 inches 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 brings it 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 Airmega AP-1512HH Mighty, our top pick, despite the AC5900WCA’s slightly lower CADR numbers. And we like the AC5900WCA’s clean looks and its 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 this model to be much louder than the AP-1512HH, measuring 47 decibels, versus 39, on its quiet/medium setting, and the quality of the sound was rough and whooshy, versus the AP-1512HH’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 AP-1512HH) on top of its much higher energy consumption.

The Levoit LV-H133 is another competitor to the Coway AP-1512HH, and it produced similar test results—98.8% and 92.9% reduction in particulates on high and medium, respectively, 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 in its CADR specs than our small-space pick, the Levoit Core 300, and it produced notably poor results in our tests, achieving a reduction of particulates of just 58.0% and 59.2% on high and medium, respectively, versus the Core 300’s 97.4% and 92.6%.

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, respectively, 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+ comes out on top on cost, as it typically sells for $300 versus the Airmega 400’s usual price of $500.

The mechanically identical Coway Airmega 400S, a “smart” version of the 400, costs a bit more and has a very basic app whose terms of service ask for unnecessarily intrusive permissions. We don’t find it worth the money or the security concerns if you’re seeking a smart purifier with remote functionality and additional information; check out the Mila instead.

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 Air Purifier Tower had much lower specs than our top pick, the Coway AP-1512HH, yet at $400 it cost twice as much. The Air Purifier Round Console was also weaker on specs and higher priced than the Coway model, at $300.

The Inofia PM1320 claims to work in rooms as large as 800 square feet. Based on its specs, we determined that 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 the much cheaper Coway Airmega AP-1512HH Mighty.

Winix’s HR900 Ultimate Pet Air Purifier has far 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 AP-1512HH. For that price, though, you get a machine that’s barely a third as capable: The Hathaspace purifier produces 2 air changes per hour in a 350-square-foot room, whereas the AP-1512HH delivers 5.7 ACH.

Dyson calls the Dyson 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, an 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 a true-HEPA machine; 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 Airmega AP-1512HH Mighty, has a CADR of 112, 117, and 95 on dust, pollen, and smoke, respectively—in every case less than half the Coway model’s CADR ratings, and below those of even our top pick for small rooms, the Levoit Core 300. 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 Blueair 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 attributes. 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 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, 10 inches wide, and 18 inches deep. 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 a former budget pick, the GermGuardian AC4825. Although the AC4825 performed well, it costs more to maintain than our current budget pick, the Levoit Core 300, because of its higher energy consumption—52 watts on medium, versus the Core 300’s 34.6 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 92.6% reduction that our small-space pick, the Levoit Core 300, achieved on medium.

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 much less.

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—as tall as 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.

In 2017, we 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—and we tested it on both functions in the lab and in the real world. John Holecek further tested it for VOC removal in the lab, considering that Dyson had implemented an upgrade of its VOC filter since our 2016 test of its predecessor. In every case the HP02 offered disappointing performance relative to our top pick. Considering its high up-front cost and relatively weak performance, we can’t recommend it.

In addition to the above 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. We have not tested the newer Rabbit SPA-780A.

Although the Bissell air400 has specs comparable to those of the Coway Airmega AP-1512HH Mighty, it typically costs over $100 more, and at the time of our research it had relatively few reviews on Amazon and on Bissell’s own site.

The GermGuardian CDAP4500 is a small-space unit that usually costs $150 or so—more than our pick in that category, the Levoit Core 300—mostly because it offers Wi-Fi connectivity, which isn’t useful or necessary.

The Rabbit Air BioGS 2.0 fails our 4 ACH limit for a standard-size room and usually costs more than our top pick from Coway.

The Alen BreatheSmart FIT50 and T500 are specced for standard usage and as a budget or small-room choice, respectively—but they usually cost at least twice what our picks in those categories do.

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 Levoit LV-PUR131 has budget specs but typically costs twice as much as our budget pick.

The Oransi OV200 has budget specs, draws as much as 60 watts (our budget pick draws 34.6 watts on medium), and usually costs much more than our budget pick.

Although the QuietPure Home Air Purifier offers specs similar to those of our also-great pick for large rooms, the Blueair Blue Pure 211+, it often costs more.

The GermGuardian AC4100 “desktop” air purifier doesn’t meet our 4 ACH minimum for small spaces.

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 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 purifier 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 usually 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 that feature for two reasons. First, there’s no way to tell whether the sensor that 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 bore 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 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 dare to push a few months beyond the stated filter lifespan, it’s likely not a crisis.

This article was edited by Harry Sawyers.