The Best Air Purifiers To Filter Out Dust, Dander, and Viral Particles

They really do work. When used correctly.

Originally Published: 
Alen air purifier for your home, on a green backdrop.

Last spring, if you told your buddy you were getting an air purifier for your house to stop the spread of COVID-19, he’d probably have given you a sideways look and asked if you considered disinfectant spray instead. But as we learn more about the novel coronavirus and how it spreads, the best air purifiers, while not a silver bullet, can be an additional weapon in your arsenal. Especially given that respiratory droplets in the air pose a very real threat. A great HEPA air filter for your homecan actually suck those bastards right out of the oxygen that you and your family breathe.

“Air purifiers can absolutely filter the virus particles from the air,” he says. “There is a whole lot of misinformation going around about whether they really work or not—the answer is, they do,” says Jeffrey Siegel, Ph.D., a professor of civil engineering at the University of Toronto who specializes in indoor air quality.

But that doesn’t necessarily mean they reduce your risk of contracting COVID, he points out. Presumably, if your purifier is filtering the virus out of the air in your house, that means you or someone you live with is already infected. Still, if you want an additional layer of virus protection when faced with, say, a visiting neighbor or your kid’s playdate, what should you look for in an air filtration system?

How Air Filters Work

There are two basic types of home air filters. If you’re using a central air system (HVAC), you’ll want filters with a high Minimum Efficiency Reporting Value, or MERV, number. This refers to a filter’s ability to capture particles between 0.3 and 10 microns in size, according to the U.S. Environmental Protection Agency. “The MERV scale rates filters on what fraction of what size particle they capture,” says Max Sherman, Ph.D., the residential team lead on the Epidemic Task Force for ASHRAE (American Society of Heating, Refrigerating and Air-Conditioning Engineers) in San Francisco. “The MERV scale goes from 1 to 16, with 16 being the highest. ASHRAE recommends MERV 13 or higher for COVID-19 purposes.”

If the air purification system you’re looking at is a stand-alone unit—a box-like device that you can move around your house from room to room—you want to make sure your filters are HEPA-certified. (HEPA stands for high-efficiency particulate air filter.) “The way HEPA works is simple,” says Jose-Luis Jimenez, Ph.D., a professor of chemistry at the University of Colorado, Boulder, who specializes in atmospheric particle characterization. “It’s a box with a fan that takes air from the room and pushes it through a filter. Particles in the air get trapped and stay on the filter while clean air is circulated back into the room.”

What makes HEPA filters the gold standard? They are designed to capture 99.97 percent of particles that are 0.3 micron in diameter by snaring them in a web of fibers that are finer than a strand of human hair. But HEPA filters can also capture bigger or smaller particles that crash into the filter structure as they ping back and forth in the air. In fact, a NASA study found HEPA filters effectively capture particles down to the size of .01 microns. Which begs the logical question: What size is the novel coronavirus? Answer: The virus itself is only 0.125 microns in size, but “it’s misleading to talk about it that way,” says Jimenez. “The virus is never naked in the air, it’s contained in respiratory droplets that are much larger.”

Bottom line: A HEPA filter is designed to catch particles as small as the virus itself and as large as the respiratory droplets it travels in. It is generally considered more effective than MERV filters, but often HEPA filters won’t fit an HVAC system, or will restrict the airflow to such a degree that the air doesn’t circulate at all, so you’re better off with a high MERV number filter for central AC.

Choosing Your Air Purifier

So far, so good. Still, it’s not a one-HEPA-fits-all world out there, and knowing the specifics of what to look in an air purifier for makes all the difference in whether you’re getting the right one for your home. Start with these tips:

Check out the CADR rating. CADR stands for clean-air delivery rate and it refers to the speed with which the filtration device can remove particles from the air. Specifically, it measures the cubic feet per minute of clean air that your air purifier can produce when set to its highest speed. CADR ratings of 300 are good, but above 350 is preferable. “The higher the number the better,” says Sherman.

Choose the right size. The air purifier for your bedroom may work great, but if you put it in your much-larger living room, it will struggle. As a rule of thumb, “choose a device that says it works for a space double the size of the room you’re putting it in,” says Siegel. “So if the manufacturer says it cleans 800 square feet, divide by two and use in a space that’s 400 square feet.” That helps in two ways: First, the air will be cleaned twice as often every hour. Secondly, some filtration systems can generate enough noise to convince you that you’re living next to an airport runway—a major deterrent to using them when you’re in the room. By choosing a larger air purifier, you can run the machine on lower settings, mitigating some of the sound.

Place it in an ideal spot. The best air purifiers in the world will do little good if the particles in the air don’t reach them. Out of all the things you should be concerned with, this may be the most important. Locate your air purifier away from furniture and curtains that might block the path of air travel, and toward the center of a room where it is equal distance from all walls. Or, if someone in your family is sick, says Siegel, place the machine closer to their chair or bed, and elevate it to table-top height since putting it on the floor runs the risk of stirring up particles that may have fallen there.

Make sure it’s really HEPA. These are the top-of-the-line for air filtration, but a lot of companies will try and confuse you with words like “HEPA-style” and “HEPA-type.” Not everything labeled HEPA is really HEPA, cautions Siegel. Don’t be fooled. You’re smarter than that. Look for the words “True HEPA Filter” and “99.97 percent filtration” to be sure.

The Best Air Purifiers For Your Home

With all this in mind, are some air purifiers more up to the task than others? For sure, say experts, who recommend using a reputable third-party source to choose one for your home. (Note that the air purifiers were not tested for removing the coronavirus, and no such information currently exists for these devices.)

Finally, a word to the wise: The most expensive air purifier in the world is no substitute for the free advice you’ve been hearing for months: Cover your face and keep your distance to stay safe from COVID. “Air filters are an additional step for risk reduction, but not the main one,” stresses Siegel. “Masks and distancing are the first things to consider if you’re trying to lower your risk.” Remember, if your air purifier is filtering out the virus, that means the virus has already somehow found its way into your home.

If that’s the case, you may be wondering, is it really worth getting a home air purifier? Look at it this way, says Sherman: “Better filtration is a no-regrets policy. Lowering the amount of particles in the indoor air may be the single biggest thing we can do as a population to improve our indoor air quality.” Best case scenario, adds Siegel, you K.O. the coronavirus. Worst case? “You’re purifying the air you breathe, which we know improves your cognitive functioning, respiratory health, and sleep quality,” he says. And really, how bad could that be?

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