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Can Air Purifiers Help?
The best ways to improve indoor air are to remove the pollutant sources and ventilate with clean outdoor air. Portable air purifiers can help when those methods are insufficient or not possible. Also known as air sanitizers, air purifiers are designed to filter the air in a single room, not the entire house like an HVAC system does. And while they do help reduce indoor pollution, there are limits to what they can do.
What Air Purifiers Do Well
The air purifiers that do well in our tests are proven in our labs to be good at filtering dust, smoke, and pollen from the air. Multiple studies of portable air purifiers show that using HEPA (High-Efficiency Particulate Air) filters result in reductions of 50 percent or higher in particulate matter. In one 2018 study of about 130 households, filtration resulted in about 30 percent reduction in coarse particles, like dust.
But how does that affect health? Nearly a dozen studies, including ones conducted in Vancouver , Taipei , and Massachusetts looked at cardiovascular effects and showed improved cardiovascular health among participants. The EPA's review of eight studies focused on allergy and asthma symptoms showed modest improvements in at least one health area, such as some allergy symptoms (which vary from person to person). And asthmatic participants in a 2018 study by UC Davis reported a 20 percent reduction in clinic visits.
Still, the scientific and medical communities can’t definitively link the use of air purifiers to health benefits because reported health benefits are inconsistent among participants and there have been very few long-term studies. Plus, some studies had other variables at play, such as the regular use of a vacuum cleaner (CR can help you choose one of those , too), pillow covers, and the removal of pets from the bedroom, all of which can affect results.
What Air Purifiers Don't Do
An air purifier can only remove allergens while they’re floating in the air. Larger, heavier allergens, such as mites, mold, and pollen, settle to the ground so quickly that the air purifier can’t capture them in time.
What We Don't Yet Know
Radon is another blind spot for air purifiers and other air cleaners, according to the EPA: Studies are inconclusive on air purifiers' ability to tackle this dangerous gas. And in fact, there is insufficient research of air purifiers that address gaseous pollutants as a group, so it's unclear how effective air purifiers are. There is also limited data on the effect of ionizer air purifiers on health. Which brings us to another important consideration: the various kinds of air purifier technology available.
Air Purifier Ratings by Consumer Reports
Types of Air Purifiers
There are several technologies air purifiers employ for tackling indoor pollution. Some work better than others . Some can actually be bad for your health.
Mechanical filters. This is the type we test. Air purifiers with pleated filters use fans to force air through a dense, pleated web of fine fibers that traps particles. Filters with very fine mesh are HEPA (High-Efficiency Particulate Air) filters—those certified to collect 99.97 percent of particles of a certain size (0.3 microns in diameter—smoke and paint pigments, for example). HEPA filters can remove larger particles, too, including dust, pollen, and some mold spores while they're suspended in the air. (Note that some filters labeled "HEPA-type" or "HEPA-like" have not been certified to meet the requirements of a true HEPA filter, but may still perform adequately in our tests.)
As for limitations, mechanical filters don't help with gases or odors. And they can be expensive to maintain. Mechanical filters need replacing every six to 12 months, and can cost up to $200 per filter but typically max out at $80.
Activated carbon filters. Rather than catch particles like mechanical filters, sorbent filters use activated carbon that can adsorb some odor-causing molecules from the air. They may also tackle some gases, but they're not particularly effective against formaldehyde, ammonia, or nitrogen oxide. Since they don't combat particles, many air purifiers will include both an activated carbon and a pleated filter for catching particles. Activated carbon gets saturated faster than a pleated filter, though, and requires replacement more frequently—every three months as opposed to every six to 12 months for pleated filters. And be prepared: Activated carbon filters cost up to $50 each.
CR does not currently test for odor removal, but we did conduct a one-off test in 2008 with five air purifiers that made odor-removing claims. For this test, we assessed how well these machines removed cooking odors. The results: Only two devices were able to do so because they used very large and thick carbon filters.
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 them. 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 0.05 parts-per-million limit 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. Studies also show that ozone has been linked to decreases in lung function and increased risks of throat irritation, coughing, chest pain, and lung-tissue inflammation. Ozone might also worsen asthma, emphysema, and bronchitis, according to the EPA.
Electronic air purifiers. Electrostatic precipitators and ionizers charge particles in the air so they stick to plates on the machine or to nearby surfaces by a magnetic-like attraction. CR doesn't typically test them or recommend them because they can produce ozone.
Ultraviolet Germicidal Irradiation (UVGI). Some air purifiers claim to kill airborne viruses, bacteria, and fungal spores with UV lamps. But some bacteria and mold spores 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 portable UVGI air purifiers—to be effective. CR does not test UVGI technology, though some mechanical air purifiers we test may have the function.
Photocatalytic Oxidation. PCO uses ultraviolet radiation and a photocatalyst, such as titanium dioxide, to produce hydroxyl radicals that oxidize gaseous pollutants. Depending on the pollutant, this reaction can sometimes generate harmful byproducts such as ozone, formaldehyde, nitrogen dioxide, and carbon monoxide. CR does not currently test PCO technology. There have been few field investigations done on the effectiveness of PCO air purifiers, but one laboratory study conducted by Syracuse University researchers reported that the devices did not effectively remove any of the volatile organic compounds (VOCs) typically found in indoor air.
Air Purifier Ratings
How Consumer Reports Tests Air Purifiers
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 micron and up to 1 micron—a range that includes dust mite allergens, cat allergens, smog, smoke, and atmospheric dust. We don’t measure for particles larger than 1 micron, such as pollen, because any air purifier that scores well in our tests should also be able to handle larger airborne particles.
Since air purifiers typically have several speed settings, we test for dust and smoke removal both on the highest speed and at a lower speed (not exceeding 50 decibels). We also measure noise levels at every speed a machine has. Since air purifiers must be on at all hours, we calculate annual operating costs, which include filter replacements and energy use to run the machine 24 hours a day for an entire year.
The very best models in our tests effectively clean the air of dust, smoke, and pollen. CR Recommends 14 models in our air purifier ratings , and all but one use a HEPA filter; a handful also have carbon filters.
Best and Worst Air Purifiers from CR's Tests
What to Consider While Shopping for an Air Purifier
Cost of replacement filters. As a general rule, you should replace filters (or clean those that can be) every 6 to 12 months for pleated filters and every 3 months for activated carbon filters. Most of the units we test have an indicator that lets you know when to change (or clean) the filter. The costs of filters vary widely, but in our tests of large air purifiers, they range from $20 to over $200 a pop. Filters with odor-removing carbon can cost as much as $50.
Certifications. There are a couple of labels you may want to look for on the packaging. The first one is the Energy Star logo. Air purifiers must run around-the-clock to be effective, and you should factor in the energy cost when you shop. Energy Star certified purifiers are 40 percent more energy-efficient than standard models.
You may also see an AHAM Verifide seal, which means that the Association of Home Appliance Manufacturers has tested the model. While voluntary, many air purifiers have undergone AHAM's certification program, which provides Clean Air Delivery Rates (CADR) and room size guidelines on the seal.
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. Portable air purifiers with HEPA filters often achieve the highest CADR. We deem a CADR above 240 as Excellent, 240 to 180 is Very Good, 179 to 120 is Good, 119-60 is Fair, and anything under 60 earns a rating of Poor.
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 or use the fireplace regularly, choose an air purifier that has a high CADR for tobacco smoke.
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 its test results. Also, consider sizing up. Most of the models that are suitable for large rooms (350 sq.ft and up) still work well at lower (quieter) speeds, which is nice for when you're watching TV or sleeping.
Noise. Judge an air purifier not just by how well it performs, but by how well you'll be able to live with it. These machines should always be running, so ideally they should also be quiet (for reference, a noise rating around 50 decibels is roughly equal to that of a refrigerator). You may be able to find how many decibels a model operates at on its packaging or website listing before you buy. Or check our air purifier ratings ; we rate models on noise levels during the high-speed setting and lower speed settings.
Other tips for minimizing noise from an air purifier: run the unit on the high setting when you're not in the room, and turn it down to low when you're nearby. Or buy an air purifier certified for a larger area so that even at a low speed, it filters more air.
Air Purifier Features to Look For
Below are several features worth looking for on your next air purifier.
The reusable filters collect large particles before they reach the primary filter, potentially extending its life and saving you money on filters.
Filter Service Indicator Light
It will flash when it's time to replace (or clean) the filter. A clogged air purifier won't work, so you need to change the filter regularly.
These particle counters can detect how polluted the air is and automatically adjust the air purifier's cleaning speed accordingly.
Carrying Handles and Wheels
Most portable air purifiers weigh from 10 to 20 pounds. If you plan on moving it from room to room, get a model with casters, which make it easy to roll.
This lets you easily adjust settings from across the room. Some models use a phone app that serves the same purpose.
Air Purifier Features to Avoid
Here are just a few features you might want to avoid.
Anything That Emits Ozone
If a unit has an ionizer (which attracts particles via an effect like static electricity), it may produce ozone. Since California has banned home air purifiers that emit ozone levels above 0.05 parts per million, they are sometimes erroneously marketed as emitting "activated oxygen," "super oxygen," or "energized oxygen." If you see any of these terms on the packaging, move on.
Most Activated Carbon Filters
Only the very large ones with several pounds of carbon granules work to remove odors, but most filters contain just a fraction of that.
These features claim to kill bacteria and mold spores, but for them to actually work on resistant strains, the UV light must be powerful enough and hold the air for a long enough duration—minutes to hours rather than the few seconds typical of most models—to be effective.
How to Get the Most Out of Your Air Purifier
Clean or replace filters regularly. As a general rule, you should replace (or clean those that can be vacuumed) every 6 to 12 months for pleated filters and every 3 months for carbon filters.
Place it wisely. If you have just one unit, place it in the room where you spend the most time. For most people, that’s the bedroom. These machines 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. For more read our article on how to choose the best air purifier for your home .
Keep your purifier running 24/7. And keep doors and windows closed while it's in use. We suggest running the unit on the high 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.
Air Purifier Ratings by Consumer Reports
Other Ways to Improve Indoor Air Quality
Vacuum regularly. No air purifiers can remove the larger allergens—dust mites and pet hair, for example—that settle on furniture and carpets unless it gets disturbed and redistributed into the air. Use a vacuum with a 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 chemical-heavy cleaning products and don't store paint, glues, or insecticides near your living quarters. For more tips read " How to Improve Indoor Air Quality ."