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Are HEPA Air Purifiers Effective Against COVID-19 Coronavirus?

Monday June 22, 2020
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Can HEPA air purifiers protect you from COVID-19? This is an important and complicated question that we think warrants a nuanced answer (which we've provided to the best of our ability below). However, if we had to distill it down we would say this: according to the best available research HEPA filter equipped air purifiers are effective at removing over 99% of viruses from the air that passes through them. Airborne transmission is now thought to be a more significant factor in the spread of the virus, suggesting that adding an air purifier to your home could be more beneficial than previously thought. However, an air purifier can only clean the air that actually reaches it, thus its real-world effectiveness is largely dictated by a number of different factors such as ventilation, airflow patterns, virus dispersal point, et cetera. Therefore, while a purifier could provide some protective benefit, it should not be used as a replacement nor in relaxation of the social distancing and sanitation guidelines outlined by the Centers for Disease Control (CDC). This means you should still limit the people entering your home to your immediate family unit, even if you have a HEPA air purifier. Additionally, if someone else must enter your home, proper distancing and facemask rules should still be followed.

Confusion Surrounding the HEPA 0.3 Micron Standard


An air filter must capture at least 99.97% of particles sized 0.3 microns to qualify as HEPA (for reference, the diameter of a human hair is generally about 50 microns, and we humans cannot see anything smaller than 40 microns). The COVID-19 virus is around 0.1 micron in size, which has led many to believe that HEPA filters would be ineffective at capturing the virus simply because it is smaller than 0.3 microns. In fact, you may have seen this stated elsewhere. While this makes intuitive sense, things at this microscopic scale are far less than intuitive.

HEPA filters can capture viruses  but can't prevent them from contaminating surfaces nor passing directly from person to person.
HEPA filters can capture viruses, but can't prevent them from contaminating surfaces nor passing directly from person to person.

The standard for HEPA filters was chosen as 0.3 microns because this size of particle is actually the hardest for the medium to filter. Particles measuring 0.3 microns are small enough to fit between many filter fibers, and are also heavy enough to have sufficient inertia to generally fly in straight lines. A straight flight path makes it more likely for a particle to pass through a filter without touching a fiber. Smaller particles have less inertia and are thus more at the mercy of microcurrents and other random forces. This causes their flight patterns to meander and resemble that of a confused hummingbird. These random and circuitous flight paths make it much more likely they will encounter a fiber when passing through a filter. Once they encounter a filter fiber that lack of inertia also makes them more susceptible to being trapped by forces like static electricity, as well as other microscopic forces. The same concept is what makes N95 masks so effective, which is perfectly illustrated in the video below:



This phenomenon is also supported by a NASA study that found HEPA filters to be quite efficient in capturing particles in the 0.1 micron size range.

What HEPA Air Purifiers Can and Can't Do


HEPA filters have been proven to capture more than 99.9% of the virus particles that reach them.. However, even if your purifier happens to be right next to a source of virus particles, many of those particles are still going to settle on and contaminate surfaces before ever making it into the filter. Even the powerful air circulation systems of airplanes are not effective enough to prevent viruses from landing on nearby people or surfaces. Therefore social distancing and disinfection remain paramount, even if you have an air purifier.

Related: The Best Air Purifiers of 2020

So, Do You Need a HEPA Air Purifier?


While HEPA filters are quite effective at capturing the virus particles that come in contact with them, we believe they would only add a marginal extra layer of protection in most situations. Additionally, an air purifier should in no way be used as an excuse to relax your adherence to any of the CDC's guidelines, as these measures offer much greater potential benefit. If you're already following these guidelines, have the means, and want to do absolutely everything possible to protect yourself and your family, an air purifier might be a worthwhile purchase. However, if the investment in an air purifier would at all hinder your ability to practice the CDC recommended social distancing then you should not buy one.

Air purifiers can often result in fewer symptoms for those with respiratory afflictions  and thus reduce overall physiological stress.
Air purifiers can often result in fewer symptoms for those with respiratory afflictions, and thus reduce overall physiological stress.

One group that is more likely to benefit from an air purifier are those with pre-existing respiratory afflictions. Air purifiers can remove potential lung irritants of all sizes from the air in your home, reducing respiratory symptoms and physiological stress. This, in turn, can reduce the overall strain on your immune system.

Related: How to Find an Air Purifier for Allergens, Smoke, and More

More Information Concerning HEPA Filtration of Viruses


COVID-19 is a fast emerging threat, thus to our knowledge no study specifically examining COVID-19 and HEPA filters has yet been conducted. However, other research indicates that HEPA filters can be quite effective in capturing similar airborne viruses. This capability is widely cited in the literature, a particularly relevant example being a study conducted by the University of Florida and the US Airforce Research Laboratory. In this study researchers fed a cloud of MS2 bacteriophages directly into a HEPA filter. The MS2 bacteriophage is a virus that infects bacteria and occupies a similar size range as the COVID-19 virus. It was found that more than 99.9% of the MS2 bacteriophages were caught by the HEPA filter. Due to the size similarities of the COVID-19 virus and the MS2 bacteriophage we can expect HEPA filters would catch many COVID-19 particles as well.

Conclusion


While HEPA filters can capture the vast majority of virus particles they encounter, they likely provide relatively little protection against infection because of the multitude of variables encountered in real-world scenarios. Additionally, while purifiers could add some extra protection in certain situations, they should not be used as a replacement for any social distancing or sanitation guidelines put in place by the CDC or state and local governments.

At TechGearLab we are committed to providing the best possible information to our readers, and that mission now feels more poignant than ever. If you have any questions about how consumer electronics can or cannot be of service as we all react to the global pandemic, please feel free to reach out to us. We'll do our very best to collate the best available research and provide you with a meaningful and actionable answer.

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