Air Purifier Buying Guide

Portable room air purifiers are designed to filter the air in a single room. They’re separate from whole-house air purifier systems and air filters, which are integrated into a home’s heating, ventilating, and air conditioning system and designed to clean the air in the entire house.

Think of a room air purifier as a supplemental unit, like a space heater in the context of a whole-house heating system, explains Misha Kollontai, who oversees testing of air purifiers at Consumer Reports. While your house might feel sufficiently warm, you might have a particularly drafty room with old, poorly sealed windows; placing a space heater there would make the room more comfortable. Similarly, he says, "a whole-house system will work at filtering all the air that passes through it via the HVAC system. But if you’re sitting next to a fireplace in the living room for extended periods of time, a room air purifier there may not be a bad idea." A room air purifier may be worth it too, say, in a bedroom, if you sleep with your pet.

An air purifier removes allergens only while they’re floating in the air. Once they’ve settled to the ground (as is often the case with heavier particles, such as large pieces of dust and pollen), you’ll need a vacuum cleaner.

Studies of room air purifiers show that using HEPA filters—filters with very fine mesh, certified to collect 99.97 percent of particles of a certain hard-to-capture size (0.3 micrometers in diameter)—can be quite effective at removing many of the most common household irritants. These include tiny viral droplets, particulate matter (such as from cigarette smoke and burning wood), pet dander, dust, and dust mites. For more details, see our article on what, exactly, an air purifier can catch.

Different air purifiers work using a range of technologies. A few are helpful. Others are ineffective, or even potentially harmful to your health.

Mechanical filters: These purifiers use fans to force air through a dense web of fine fibers that trap particles. Filters with very fine mesh are called HEPA filters. While they work on microscopic particles, they can also remove larger particles (including dust, pollen, and some mold spores) when they’re suspended in the air. (Some filters are labeled “HEPA-type” or “HEPA-like”—these have not been certified to meet the requirements of a true HEPA filter but may still perform adequately in our tests.) Mechanical filters don’t help with gases or odors. And they can be expensive to maintain. Mechanical filters need to be replaced every six to 12 months; they can cost upward of $200 per filter but typically cost no more than $80.

Activated carbon filters: Unlike mechanical filters, these filters use activated carbon to capture certain types of gases, including some odor-causing molecules. But they’re not particularly effective against formaldehyde, ammonia, or nitrogen oxide. Because activated carbon filters don’t combat particles, many air purifiers will have both an activated carbon filter and a mechanical filter. Activated carbon filters get saturated faster than mechanical filters, though, and require replacement more frequently—every three months, as opposed to every six to 12 months for mechanical filters. Make sure to budget for replacements accordingly: Activated carbon filters usually cost up to $50 each. 

Ozone generators: These machines produce ozone, a molecule that can react with certain pollutants to alter their chemical composition. This can result in dangerous indoor air quality, and CR does not recommend these types of air purifiers. Makers of ozone generators often claim that the devices emit safe levels of ozone, but in the past, our tests found that even at low settings, some ozone generators quickly exceeded the Food and Drug Administration’s limit of 0.05 parts per million for medical devices. Plus, studies reviewed by the EPA have shown that low levels of ozone—the chief ingredient of smog—don’t effectively destroy indoor pollutants. Research also shows that ozone has been linked to decreased lung function and increased risks of throat irritation, coughing, chest pain, and lung tissue inflammation. Ozone exposure might also worsen asthma, emphysema, and bronchitis.

Electrostatic precipitators and ionizers: In these electronic models, particles in the air become charged so that they stick—magnet-like—to plates on the machine or to nearby surfaces. CR doesn’t typically test electronic air purifiers nor recommend them because they can produce ozone.

Ultraviolet germicidal irradiation (UVGI): Some manufacturers claim that their air purifiers kill airborne viruses, bacteria, and fungal spores with UV lamps. But they might miss certain bacteria and mold spores that are resistant to UV radiation. To work, the UV light must be powerful enough and the exposure must last long enough—minutes to hours, rather than the few seconds typical of most UVGI air purifiers—to be effective. CR does not test UVGI technology, though some mechanical air purifiers we test may have the added function.

Photocatalytic oxidation (PCO): Some air purifiers use ultraviolet radiation and a photocatalyst, such as titanium dioxide, to produce hydroxyl radicals that oxidize gaseous pollutants. Depending on the pollutant, this reaction can generate harmful byproducts, such as ozone, formaldehyde, nitrogen dioxide, and carbon monoxide. CR does not currently test air purifiers with PCO technology. There have been few field investigations exploring the effectiveness of PCO air purifiers, but one laboratory study, conducted by researchers at Syracuse University in New York, reported that the devices did not effectively remove any of the VOCs typically found in indoor air. 

Photoelectrochemical oxidation (PECO): This variant of PCO emerged in 2017 from the manufacturer Molekule. The Molekule Air purifier did not score well in our tests for dust, smoke, and pollen removal. Since then we’ve also tested the more expensive Molekule Air Pro, which performed better at removing contaminants on its highest setting but did not impress in CR’s other air-purifier test categories, nor did it rate well in our CR member survey. 

To see how well these machines clean the air, we inject smoke and dust into a sealed chamber and use a particle counter to measure the change in air particle concentration in the room as the test model runs for 15 minutes. 

We test using particles as small as 0.1 micrometer and up to 1 micrometer, a range that includes dust mite allergens, cat allergens, smog, smoke, and atmospheric dust. We don’t measure for particles larger than 1 micrometer, such as pollen, because any air purifier that scores well in our tests should also be able to handle larger airborne particles.

Because most air purifiers have several speed settings, we test for dust and smoke removal both on the highest speed and at a lower speed that runs at a noise level no louder than 50 decibels. We also measure noise levels at every speed setting that a machine has. And because air purifiers must be running at all hours to be effective, we calculate annual operating costs, which include filter replacements and energy use to run the machine 24 hours a day for an entire year.

Owner satisfaction and reliability ratings are also included in a model’s Overall Score. These ratings are based on Consumer Reports’ 2022 Summer Survey of 8,377 air purifiers purchased between 2012 and 2022. The very best models in our tests effectively sanitize the air of dust, smoke, and pollen, and receive high marks for predicted reliability and owner satisfaction. 

CR recommends more than three dozen models in our air purifier ratings, and most use a HEPA filter; a vast majority also have carbon filters to help assist in the removal of odors. These models meet Consumer Reports’ criteria for safety, performance, value, and reliability. For more information, read our article on the best and worst air purifiers of the year.

Cost of replacement filters: As a general rule, you should replace filters (or clean those that can be vacuumed) every six to 12 months if they are pleated and every three months for activated carbon filters. Most of the units we test have an indicator light that lets you know when to change (or clean) the filter. The costs of filters vary widely: In our tests of large air purifiers, they range from $20 to more than $200. Filters with odor-removing carbon can cost as much as $50. 

Clear Air Delivery Rate (CADR): This value is provided by air purifiers tested by the Association of Home Appliance Manufacturers. Many air purifiers have undergone AHAM’s voluntary certification program, which provides room size guidelines along with the CADR on its AHAM Verifide seal. The CADR reflects, in cubic feet per minute, the volume of clean air that an air purifier produces on its highest speed setting. For example, a purifier with a CADR of 250 for dust particles reduces particle levels of dust to the same concentration that would be achieved by adding 250 cubic feet of clean air each minute. The higher the CADR, the faster and more efficient the air purifier is. Room air purifiers with HEPA filters often achieve the highest CADR. There are different CADR ratings for removing tobacco smoke, dust, and pollen. Focus on the CADR for your main pollutant of concern. For instance, if you live with a smoker, choose an air purifier that has a high CADR for tobacco smoke. 

Energy Star certification: Air purifiers must run around the clock to be effective, so you should factor in the energy cost when you shop. Energy Star certified purifiers are 40 percent more energy-efficient than standard models. 

Room size: If an air purifier has an AHAM Verifide seal, you can trust that the unit can handle the suggested room size listed on the seal. Be wary about manufacturers’ claims, though. We have tested many air purifiers that are not suitable for their claimed room sizes. You can check our ratings to see what room-size range we suggest for each model based on our test results. Also, consider sizing up: Most models suitable for large rooms (350 square feet and larger) can also work well for smaller rooms at lower speeds. Lower speeds tend to be quieter—which is nice for when you’re watching TV or sleeping.

Noise: Judge an air purifier not just by how well it performs but also by how well you’ll be able to live with it. Because these machines should always be running, ideally they should also be quiet. (For reference, a noise rating around 50 decibels is roughly equal to the hum of a refrigerator.) You may be able to find a model’s decibel levels on its packaging or website listing before you buy it. Or check our air purifier ratings; we rate models on noise levels at both high- and low-speed settings.

Clean or replace filters regularly. An air purifier can’t run efficiently if it has a dirty filter. Typically, you should replace filters (or clean those that can be vacuumed) every six to 12 months for pleated filters and every three months for activated carbon filters.

Place it wisely. If you have just one unit, put it in the room where you spend the most time. For most people, that’s the bedroom. (Some units can be heavy and clunky to move around, so if you want an air purifier in multiple rooms, you may want to buy a unit for each room.) Make sure to place the air purifier in a spot where nothing can obstruct airflow—away from curtains, for instance.

Adjust the speed. To avoid noise disruptions, we suggest running the unit on its high-speed setting when you’re not in the room and turning it down to low when you’re nearby. Or buy an air purifier certified for a larger area so that you can run it on a low speed and still have it work effectively. 

Vacuum regularly. Air purifiers can’t remove the larger allergens—dust mites and pet hair, for example—that settle on furniture and carpets unless they get disturbed and redistributed into the air. Use a vacuum cleaner with HEPA-certified filtration once or twice a week to clean floors and furniture.

Use an exhaust fan in the kitchen. Do the same in bathrooms and laundry rooms. 

Stop smoking indoors. That also goes for burning candles and wood fires. 

Ventilate. Open your windows on nice days to let in clean, dry outdoor air. If pollen or related allergies keep you from opening windows, run your air conditioner or forced-air cooling system with a clean air filter.

Reduce the use of chemicals. Limit the use of chemical-heavy cleaning products, and stow house paint, glues, and insecticides in a basement or another area that’s away from where you spend most of your time at home.