Do Hepa Air Filters Work

Air purifiers with HEPA filtration efficiently capture particles the size of (and far smaller than) the virus that causes COVID-nineteen, then the answer is yes. Furthermore, on October 5, 2020, the CDC changed its stance on how the virus is transmitted, and now says it "tin exist spread by exposure to virus in small droplets and particles that tin linger in the air for minutes to hours." In short, the CDC now acknowledges that the virus can spread via the air. That'south a major adjustment of its prior position: that direct person-to-person contact, including via larger respiratory droplets that do non travel far or linger in the air, was the main vector, and that airborne (a.grand.a. aerosol) transmission was not a vector, period. Evidence for airborne transmission has been mounting since the spring; to catch up on the class this inquiry has taken, read over University of Colorado-Boulder aerosols scientist Jose-Luis Jimenez's summary in Time. And information technology's worth noting that on September xviii, the CDC published—and three days later retracted, citing errors in an internal review process—a version of its guideline that stated flatly that inhalation of aerosolized respiratory aerosol "is thought to be the primary way the virus spreads."

Back to purifiers: The virus that causes COVID-nineteen is approximately 0.125 micron (125 nanometers) in diameter. It falls squarely within the particle-size range that HEPA filters capture with extraordinary efficiency: 0.01 micron (10 nanometers) and in a higher place. Many media outlets have incorrectly stated that HEPA filters don't filter below 0.three micron and therefore could not capture airborne coronaviruses. That'south wrong. This NASA study of HEPA filtration is quite technical, just the graph on page 7 and the preceding paragraph practice a good job of explaining why HEPA filters are actually nearly efficient—near 100% at 0.01 micron—at capturing ultrafine particles below the 0.3-micron HEPA exam standard.

a Coway air purifier on a rug, between a plant and a chair. — Photo: Sarah Kobos

This means HEPA purifiers would efficiently capture viruses (and any aerosolized aerosol of saliva and mucus that contain them) that are drawn into their filters. In its communication on cleaning and disinfecting homes during the pandemic, the CDC recognizes as much: "When used properly, air purifiers can aid reduce airborne contaminants, including viruses, in a home or confined infinite." And in its guidance for health-care personnel, the CDC states that air from rooms where COVID-xix patients are being isolated "should be exhausted directly to the outside or be filtered through a high-efficiency particulate air (HEPA) filter directly before recirculation," and advises health-care workers to "consider the addition of portable solutions (e.g., portable HEPA filtration units) to augment air quality in areas when permanent air-handling systems are not a feasible option." Beyond this, medical facilities have employed HEPA filtration since the mail–Globe War Two era to capture airborne pathogens, and, during the COVID-19 pandemic, many school systems are using them to broaden HVAC filters and natural (window) ventilation. (The New York City public schoolhouse system, the nation's largest, has purchased 30,000 every bit of November 2020, for example.)

What's less clear is whether a HEPA purifier would catch the virus prior to the betoken of inhalation. If yous're sitting next to someone who has COVID-19, for example, an air purifier on the far side of the room is unlikely to protect yous adequately. That raises some other unanswered question about how constructive an air purifier tin can be: What level of exposure to the virus causes an infection to begin with? We are following this topic closely, and nosotros appreciate our readers' ongoing support in helping us maintain accurate, current information.

But even if you determine to use an air purifier as a protective measure, nosotros recommend that you also continue to closely follow the CDC's other longstanding advice, including social distancing, wearing a face covering outdoors, washing your easily ofttimes, and treating frequently touched surfaces with disinfectants. Equally the CDC writes: "The best way to prevent illness is to avoid being exposed to this virus."