Can an Air Purifier Protect Me From the Coronavirus? Image: An air purifier in a bedroom.

Running an air purifier at home can be a good idea anytime, to help filter out indoor allergens and pollutants like fumes from cooking and cleaning products. And that's especially true now, when so many people are stuck indoors 24/7 because of the coronavirus pandemic. 

But you may also be wondering if an air purifier can prevent COVID-19 by capturing virus particles that could be traveling in the air.

We spoke with air quality and virology experts, and asked CR's own experts to weigh in. The consensus is that while air purifiers probably don't offer much protection in most circumstances, they may be worthwhile in a few specific ones.

If someone in your household is sick with COVID-19, running an air purifier in their quarantine room may help protect other family members or caregivers. The same goes for healthcare workers who are self-quarantining when they come home.

More on air purifiers and the coronavirus

Our understanding of how the coronavirus spreads is evolving, but the current thinking is that it travels via droplets expelled from the body through coughing, talking, and breathing. While most of these droplets fall to the ground quickly, some research suggests smaller particles may remain in the air for longer.

But even if you live with a healthcare worker or someone sick with COVID-19, before you run out to buy an air purifier, our experts say that simply opening up the windows in your home to let in fresh air will help dilute indoor contaminants—including virus particles. 

If airing out the room isn’t an option, you could try using a high-efficiency particulate air (HEPA) purifier.

“We don’t yet have direct evidence that filtration works to reduce transmission of the novel coronavirus,” says Jeffrey Siegel, an indoor air quality expert and professor of civil engineering at the University of Toronto who has researched portable air purifiers with various airborne particles.

“But we can infer from what we know for similar viruses, like SARS," he says, that there is reason to think air purifiers might help in some situations. 

In 2003, during the SARS outbreak, the Hong Kong Hospital Authority recommended hospitals use portable air purifiers with HEPA filters to help reduce transmission to healthcare workers if isolation wards were not available. In the U.S., the CDC also recommended the use of HEPA purifiers to help reduce viral concentrations of the SARS virus in the air when properly ventilated hospital rooms weren’t available.

Recent research published in the Journal of Infectious Diseases and under review at BMC Infectious Diseases suggests that air filtration can reduce the risk of transmission of measles and influenza. 

“In theory, if an air purifier removes viruses from the air, it reduces concentrations in the room and thus reduces the potential for exposure,” says Linsey Marr, an environmental engineer and professor at Virginia Tech who specializes in airborne disease transmission, air quality, and nanotechnology. “So there is a mechanistic reason to think that air purifiers could help reduce transmission.”

Read on to find out how air purifiers can capture the coronavirus, how to use an air purifier to help limit the spread of COVID-19 at home, and details on the air purifiers from CR’s tests that may work best in this very specific scenario.

How an Air Purifier Could Capture the Coronavirus

HEPA filters are very effective, certified to capture 99.97 percent of particles that are precisely 0.3 micron in diameter. (Particles that size are perfectly suited to maneuver through the filter’s fibers, while larger and smaller particles, because of the various ways they move in the air, crash into the structure.) 

The novel coronavirus itself is 0.125 microns, but Marr says the droplets it travels in—when people cough, talk, or breathe—initially are larger, around 1 micron. That's a size easily captured by HEPA filters.

James Dickerson, CR’s chief science officer echoes the consensus that air purifiers could help in some situations, but with a caveat: “HEPA filters are very efficient at catching coronavirus-size particles, but the particles must first physically travel to the filter,” he says.  

That means an air purifier has to be capable of consistently drawing in enough air to reduce the amount of virus particles in the air. The faster an air purifier can cycle air through the filter, the better its chances of catching virus particles. You can see how fast an air purifier cleans the surrounding air by looking for its CADR (clean air delivery rate) number on the packaging.

CADR reflects, in cubic feet per minute, the volume of clean air that an air purifier produces at its highest speed setting. At lower speeds, the rate a machine is able to clean air decreases. The packaging should have three CADR ratings, one for smoke, dust, and pollen, which represent small, medium, or large particles, respectively. For example, a purifier with a CADR of 250 for smoke reduces smoke particle levels to the same concentration that would be achieved by adding 250 cubic feet of clean air each minute. (Smoke particles are similar in size to the smallest virus droplets while larger droplets are closer to the pollen size range.) 

Based on CR's lab tests of air purifiers, we recommend looking for a model with a CADR over 240, which can perform roughly five air exchanges per hour in its suggested room size. In our tests, these air purifiers perform well for quickly removing particles of all sizes from the air. All the models we highlight below have a CADR over 240. 

One practical matter to consider, however, is that you may not want to run an air purifier on its highest speed setting (in order to achieve the highest CADR). Air purifiers can be quite loud, especially at higher speeds, and that can disturb the sick person’s sleep. Here at CR we measure air purifiers’ noise levels in decibels and rate that trait. The models we highlight perform well removing particles even at lower, quieter speeds.

Even the most efficient air purifiers can’t prevent some droplets from landing on surfaces, where they can live for hours or even days according to early research at the National Institutes of Health. So to help prevent the spread of the virus in your house, you should clean your home and wash your hands frequently, too.

How to Use an Air Purifier When a Family Member Is Sick

If you believe you or someone in your household might have COVID-19, follow the Centers for Disease Control and Prevention (CDC) guidelines for essential steps to take, which include how to monitor symptoms, when to seek medical help, and the proper way to isolate someone who's sick.

To use a HEPA purifier at home to help prevent transmission of the virus to other family members, Siegel suggests placing the unit three feet from the person who is sick with COVID-19. “We know that close contact is a main transmission route so I would rather people have an air purifier on low speed near the patient rather than farther away on super high speed,” he says.

Run it 24 hours a day on the highest setting that won’t disturb the sick person’s sleep. In addition, keep the air purifier separated from anything that can obstruct airflow, such as curtains or furniture, and keep the door to the room closed. When used correctly, the filter can potentially intercept floating virus particles before they reach a caregiver in the same room, says Siegel. 

Take extra precautions when handling the air purifier and changing the HEPA filter. According to early studies, the coronavirus can live on plastic and steel, both materials air purifiers are commonly made of, for up to three days. And, Siegel says, "We don’t know yet how long the coronavirus can survive on filters."

Don’t touch the air purifier while it’s in use, and when it’s time to change the filter, put on gloves and a surgical mask if you have one, take the air purifier outside, and clean and disinfectant the exterior. Then remove the filter and dispose of it in a sealed bag. If your air purifier has a fabric prefilter, wash it.

One note about advertisements you may be seeing about using air purifiers against the coronavirus: Be wary if you see products that claim they can outright prevent COVID-19 or destroy the coronavirus. 

“Some air purifiers claim to kill viruses using UV light or some kind of photocatalysis technology,” says John Galeotafiore, a director of testing at CR. “We suggest consumers take these claims with a grain of salt because there isn't enough concrete evidence yet that proves they work in these settings.”

HEPA Purifiers From CR’s Tests

Consumer Reports does not test air purifiers for virus removal, but we do perform our tests using similarly sized airborne 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). All of CR’s top-rated models have no problems trapping particles in this spectrum.

Because air purifiers typically have several speed settings, we test for dust and smoke removal both at the highest speed and at a lower speed, and we do the same for noise. Here are seven air purifiers that have high CADRs and earn an Excellent or Very Good in our particle reduction tests while being quiet—so they should help capture viruses without disturbing a sick person’s rest. 

For more information on these and other air purifiers we test, including the recommended room size for the machines below, see our air purifier buying guide and ratings. These models are listed in alphabetical order.

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The Alen BreatheSmart Classic is an air purifier made for large rooms, but this sleek model can clean the air quietly and even more quickly when used in a small room, like a bedroom. It scores an Excellent rating in our particle reduction test at high speed and a Very Good rating on its lower speed. Both speeds earn Good ratings for noise, meaning you should be able to carry on a conversation in the room.

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This Blueair Blue Pure 211+ scores Excellent ratings in both our high-speed and low-speed particle reduction tests—one of only two models to do so (the other one is the Blueair below). This air purifier is relatively quiet on its lower setting, garnering a Good for noise, but is a little loud on its highest speed setting.

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Blueair Classic 605

Price: $830

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While Blueair Classic 605’s cleaning ability is more than most people need in a bedroom, it’s the best and fastest air purifier we test, garnering Excellent ratings in both our high-speed and low-speed particle reduction tests. It’s the only model we test that earns a Very Good noise rating on its low speed while still getting superb cleaning results (at its highest speed, this model is quite noisy, though).

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Honeywell HPA300

Price: $250

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In our particle-reduction tests, the Honeywell HPA300’s air purifier scores Excellent and Very Good ratings at its highest speed and lower speed, respectively. For noise, it’s rated Good at any speed.

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SPT AC-2102

Price: $310

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In our tests, the SPT AC-2102 air purifier’s high-speed setting earns an Excellent rating for removing particles from the air, but it’s pretty noisy, garnering a Fair rating in that test. You can use it on a lower, quieter speed setting, though, which still earns a Very Good rating for particle removal.

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Winix 5300-2

Price: $150

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At high speed, this Winix 5300-2 scores an Excellent in our particle reduction test and earns a Very Good rating for noise, the only model to do so at its high-speed setting. It’s also the least expensive model on this list. We recommend operating it only at high speed because this Winix doesn’t perform particularly well for removing particles at low speed.

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Similar to the Winix 5300-2 above, we only recommend running this FresHome WACP450 on its highest speed setting, which earns an Excellent rating in our particle reduction test while scoring a Good for noise (still fairly quiet). Its efficiency for removing particles drops notably on its lower speed settings.

Editor's Note: This article has been updated to clarify the particle sizes that HEPA filters can capture and explain how the filters capture such particles.