An air purifier is a small appliance meant to remove various types of particulate matter from the air, says Robert Laumbach, M.D., M.P.H., associate professor at the Environmental and Occupational Health Sciences Institute (EOHSI) at the Rutgers School of Public Health. That includes particles that are created indoors like cigarette smoke, mold spores, emissions from stoves, and dust that’s suspended in the air, and outdoor air pollution that makes its way inside, Laumbach says. Air purifiers take in polluted air, filter out and trap particles, and then blow out newly filtered air.
There’s a variety of air purifiers out there, designed for specific purposes. “For those with allergies and eczema, for example, there are purifiers that have multiple filters to remove allergens,” says Hadley King, M.D., NYC-based dermatologist and clinical instructor of dermatology at the Weill Medical College of Cornell University. “For those with asthma that is triggered by odor and chemical pollutants, there are purifiers that have filters to remove allergens, in addition to odor and chemical filters. There are also specific filters for smoke, pets, and chemical sensitivities.” Air filters can be especially helpful for people who are allergic to dust mites and pet dander, says Bruce Prenner, M.D., board-certified allergist at Allergy Associates Medical Group in San Diego, California.
While you’ll want to choose an air purifier that is meant for filtering out the specific types of particles that you’re looking to eliminate from your home, experts do suggest some general criteria that’s important to look for in a solid air purifier. For SELF's product reviews, where we rigorously test and evaluate all kinds of wellness products to help you decide what's worth buying, we wanted to know: what criteria do experts think you should look for when evaluating a air purifier? Here are the criteria they suggested we use when testing.
Air Purifier Evaluation and Testing Criteria
“HEPA stands for high-efficiency particulate air filter and has the capability of filtering out particles that are very small (filtering 99.97% of particles down to 0.3 micrograms),” explains Rekha Raveendran, M.D., allergist and immunologist at The Ohio State University Wexner Medical Center. This type of filter has been studied extensively and is basically the gold standard for air purification. When testing air purifiers, we prioritize ones that contain a HEPA filter, or note why we're evaluating a non-ozone-producing, non-HEPA filter (more on that below).
Laumbach notes that some brands will market “medical grade” or “super” HEPA, but it doesn't mean the purifier will work any better than a regular or “true” HEPA filter. There’s no standard for this allegedly enhanced filter, but Laumbach says it’s likely more tightly woven or contains thicker webbing, which can block air from filtering through and actually make the purifier less effective. For this reason, we try to avoid products that claim to have a medical grade or super HEPA filter, and note when they make these claims.
Using an air purifier that contains an appropriately sized filter is important. Too small, and it won’t filter the air adequately; too large, and it’s just sort of overkill and a waste of electricity, says Laumbach. Air purifiers are tested and evaluated based on their clean air delivery rate (CADR), he explains. CADR is essentially a measure of the air purifier’s efficiency, or how much clean air it can deliver in a room of a specific size. Both air flow and efficiency of particle removal are used to calculate it, and it’s a standardized test done by an independent group, Laumbach says. “In the CADR certification, they give room size in square feet and the CADR that results in 12 air changes in the room per hour.” When testing air purifiers, we check the certification and made sure the air purifier is only being used in an appropriately sized room. We also note the size (i.e. the product footprint) of the purifier for its intended room and score based on whether the purifier seems an appropriate size, or too obtrusive for the space.
The filters in air purifiers need to be replaced regularly to make sure the machine keeps running properly and working effectively. When testing air purifiers, we consider the filter replacement schedule, how easy it is to remove and replace the filters, and how pricey new filters are.
Air purifiers with HEPA filters are the most studied and recommended, but other types of air purifiers do exist. An electrostatic precipitator (ESP) is another type of filter that works by electrically charging a metal surface so that it attracts particles and pulls them from the air, Laumbach says. “Those forces can pull particles from a further distance compared to other filters,” he says. Another type of electrically charged filter is known as an ionizer, which works by releasing charged particles into the air so that they can cling to pollutants and pull them to the purifier. The problem with these electronic types of filters is that they can create ozone, says Laumbach. According to the Environmental Protection Agency (EPA), ozone can damage the lungs and even relatively low amounts can cause chest pain, coughing, shortness of breath, and throat irritation. It can be particularly irritating for people with chronic respiratory diseases like asthma. When testing air purifiers that contain ESP or ionized filters, we only consider ones that have been tested and proven to not produce ozone.
If you suffer from allergies, especially if you live with an allergen (like a pet), you may want to run your air purifier throughout the day and overnight—which means noise could be a potential problem. We test noise levels of air purifiers by noting if the machine is loud enough to prevent sleep or disturb sleep throughout the night. We also compare each air purifier to another typical noise to make it clear how obtrusive it was, and use a noise app to measure decibel levels.
ESFI suggests always making sure a small appliance, such as an air purifier, has a label showing it has been tested by a Nationally Recognized Testing Laboratory (NRTL). This certification means the air purifier has undergone independent testing to ensure it meets safety standards and is free of recognized hazards that could cause injury or death, an ESFI spokesperson says. When evaluating air purifiers, we note whether the appliance has been tested by a NRTL.
ESFI recommends using all energy-efficient appliances and products to avoid drawing too much electricity and tripping circuits in your home. Efficient appliances can also help you save money on electricity costs. Air purifiers with an Energy Star rating have been independently tested and proven to save energy—Energy Star notes that certified air purifiers are almost 60 percent more energy-efficient than standard models, saving consumers about 500 kWh/year and $60 annually on utility bills. To test energy efficiency, we check to make sure that air purifiers have an Energy Star certification and note whether or not they do.
Experts Consulted for These Guidelines
- Hadley King, M.D., NYC-based dermatologist and clinical instructor of dermatology at the Weill Medical College of Cornell University
- Robert Laumbach, M.D., M.P.H., associate professor at the Environmental and Occupational Health Sciences Institute (EOHSI) at the Rutgers School of Public Health
- Bruce Prenner, M.D., board-certified allergist at Allergy Associates Medical Group in San Diego, California
- Rekha Raveendran, M.D., allergist and immunologist at The Ohio State University Wexner Medical Center
Reviews That Used These Guidelines
This is a buying and testing guide for SELF product reviews. See all our reviews here.
