Can HEPA Filters and Air Purifiers Remove COVID-19?

Data shows face masks can protect you from COVID-19, but how about air purifiers? Can an air purifier with HEPA filters remove COVID-19 and other viruses?

Can HEPA Filters Remove Viruses Such as COVID-19?

To answer this question, we need to first answer if HEPA filters can capture particles as small as viruses, such as the coronavirus. The COVID-19 coronavirus measures 0.06 – 0.14 microns in diameter.

Coronavirus virus particle size, can air purifiers capture coronavirus

HEPA filters – the workhorse of any purifier – must remove 99.97% of particles “greater than or equal to” 0.3 microns.

HEPA filter particle capture size 0.3µm; air purifiers coronavirus

But the definition only mentions particles 0.3 microns and above. What about smaller particles like the coronavirus and other viruses?  Can HEPA filters capture these?

This exact question has led to years of confusion and false advertising claims about HEPA filters, and is now leading to more misinformation about whether HEPA filters can or cannot capture and remove the coronavirus that causes COVID-19.

coronavirus size too small for masks

Why HEPA Filters are Great at Capturing COVID-19

The fact that HEPA filters are so good at removing tiny virus particles like COVID-19 is surprising. It’s surprising because our intuition about filters is wrong. Like most people, I had the intuition that HEPA filters work like a net.

HEPA filters - do they capture particles like a net?

If a particle is smaller than the holes in the net, it gets through. Makes sense! However, it turns out that particles as small as the coronavirus, and other nano-particles get captured using a scientific phenomenon called diffusion.

Learn more about the science behind diffusion and how it captures nano-particles »

Diffusion is surprisingly effective at capturing tiny virus-sized particles. According to NASA, HEPA filters capture “virtually 100% of particulates.”

NASA nanoparticles HEPA capture

Researchers at the University of Minnesota tested this question with weaker fiberglass furnace filters and higher-grade HEPA filters. In their test, they shot particles of silver from 3 to 20 nanometers at the filters (that’s roughly 5 to 30 times smaller than coronavirus particles).

HEPA Filters Capture Nanoparticles; air purifiers capture coronavirus

The results showed that filters captured 99.99% of particles smaller than 5 nanometers. Bingo! HEPA filters are incredibly effective at capturing nanoparticles–even smaller than the coronavirus.

Read More: Can UV light Kill the Coronavirus?

Do I Need a Medical Grade Air Purifier?

It may seem logical that in order to filter out viruses, a medical grade air purifier is needed. Turns out, medical grade air purifiers are more often than not a marketing gimmick. Normal, HEPA filter air purifiers can filter viruses.

Caveat: HEPA air purifiers are not a silver bullet. They can filter out viruses from the air in homes, offices and schools, but other steps such as good hygiene and disinfectants should still be used in conjunction with HEPA air purifiers.

Bottom Line: Can Air Purifiers Capture The Coronavirus?

Air purifiers that contain HEPA filters or even lower grade filters can capture virtually all sizes of solid particles, including particles 0.1 microns in diameter – or the same size as the coronavirus.

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Explore more: What types of filters do I need to protect myself from all types of pollutants?

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66 thoughts on “Can HEPA Filters and Air Purifiers Remove COVID-19?”

  1. This is a great article, but I think you should update it to make it clear that SARS-CoV-2 (and other respiratory viruses) do not travel naked through the air but rather are carried in aerosols, with approximately 85% of the total exhaled viral load contained in aerosols below 5µm in diameter. Jose-Luis Jimenez, Linsey Marr, Richard Corsi, & other world-leading experts in aerosols and IAQ put together an amazing FAQ that discusses this and many, many other questions about airborne Covid transmission. Here’s the relevant paragraph and link:

    “While the size of an individual SARS-CoV-2 virus is very small (120 nm or 0.12 microns), the aerosol in which respiratory viruses are contained are larger, albeit still small enough to remain suspended in air for long periods. A widely held misconception is that the virus is naked in the air, perhaps with some water. This has been propagated by graphics in major medical journals such as JAMA. Our best guess is that the most common aerosol size is a few microns, where the viruses comprise a very small fraction of the aerosol, as exemplified in the figure below. Aerosol size has major implications for the ability of masks and filters to remove it from the air, how deeply it will penetrate the lungs, and determines the loss rate due to gravitational settling in indoor spaces.”*YrLy9epGlHWhKPSl5JMT3w#heading=h.t3pt7ih8eldj

  2. Hi everyone.
    1. Even if HEPA catch virus particles, what next? They will stay on it, is it? HEPA would not kill virus,bacteria etc??
    2. There are air purifiers using a Thermodynamic Sterilising System (TSS) to destroy airborne mould, bacteria, viruses, dust mites, pollen and pet allergens. Air is drawn into the unit by convection and heated up to temperatures close to 200°C. This temperature effectively sterilises the air, killing harmful viruses and bacteria and destroying allergens with no residue. Air is then cooled and returned to the atmosphere.
    3. There is also plasma air purifiers, what about them??

  3. Thanks for your studies. When you refer to HEPA filters’ abilities, what grade of HEPA filter are you referring to — eg, HEPA10, 11, 12, 13, 14, etc.? I’m looking at a portable stroller filter that’s HEPA11, for example. For the microparticles where HEPA excels, are the higher numbered HEPA filters more effective?

    • The studies referred to in this post covers how MERV filters which are much less effective than HEPA filters can also capture 99% of particles as small as the coronavirus. H10, H11, H12 or H13 – they will all do a good job (>99%) of capturing the coronavirus.

      • You don’t seem to sell in the USA but what I use are cheap 20in X 4 in “Lasko” 3 speed fans with a 4 in deep MERV13 filter taped to the back. I will defer to your experience in aerodynamics but having the filter in front of the fan should cause a rebound effects and counterproductive air current inside the fan housing.

        Pulling the air eliminates some of this issue but it is likely that the fan sucks in some air from in front of itself to then throw back out.

        What do you think?

  4. Thank you very much for a great article !
    Can there be a small mechanism , preferably lightweight, which you can strap to your waist and it would filter the air and a contraption like oxygen mask be worn and which is connected to the output from the mechanism ? Basically the same concept of supplying clean air to Clean rooms but just enough for a person to breathe.I am thinking with reference to Corona virus size.

  5. Please scientifically explain how the activated carbon capture the particles that are smaller than the filtration size capacity of Hepa filter.

  6. Thanks Paddy for this great article,
    I would like to add that filtration efficiency should be rated at MPPS (Most penetrating particules size) which vary (10 nm-500 nm) with speed and type of filter (electrostatic or not). A electrostatic filter rated 99,97% at 0.3 um would not garanti the performance at 0.1 um. However, we can suppose that an efficiency of 99% will be achieve in most design.

    • Spot on Martin, you’re exactly right! MPPS isn’t always 0.3 microns, but it’s a good estimate in most cases, and is needed when running standard tests at a fixed speed (typically 5.3cm/s for HEPAs), to compare them.

  7. So are their any recommendations for a dental office other than setting up as negative air pressure rooms that would be insanely costly? Currently being bombarded by air filter buisinesses

  8. I am an oral surgeon looking for a short term fix until I can incorporate hepa filtration and negative pressure into my rooms. I have not been able to find a NIOSH classification or recommendation for any room based HEPA filtration system. It appears from your article that any air purifying system with a HEPA filter will be an improvement but do you recommend any ?

      • This is absolutely not true and there are serious consequences (risk of infecting patients) to this simplistic view. You miss two main points.

        1. particle breakthrough that is a measure and grading system separate from initial efficiency. In the real world two cartridges can have the same high efficiency rating but one will be able to hold the captured particles over time while the other will release them back into the “clean” air coming out of the purifier.

        2. the efficiency rating of the cartridges means if the filter is not sealed in the housing. If there is leakage around the cartridges (as there is with all SmartAir purifiers) the particles can and will come off of the filter face, around the housing, and leave with the “clean” air coming out the purifiers.

        In both these cases the purifier then becomes a source of particles (bacteria, viruses, etc) that could be contaminating the room every time you turn it on. This is even more likely if you use the lower grade H11 filters recommended in that article.

        • Hi Charlie, I am a dentist too and would like to know your recommendation for HEPA to decontaminate a room between patients?
          Thanks in advance

        • It would be helpful if you could cite independent research. The question is essentially if some level of filtration is better than none. There is no requirement to provide air filtration at any level in the United States in many, if not most, outpatient medical facilities. Furthermore, unless you create a negative pressure environment, there will be leakage. Its all a cost/benefit trade off.

        • I would like to know which purifier and filters you recommend. Whether it is required is not the issue. What is safest for the provider and for the patient is my priority. Thank you.

  9. Recent articles in US press have touted blue hydro polyester shop towels as n-95 equivalent filtration for home made masks. What is hydro polyester and can you weigh in on this? I’m making homemade masks. Thanks!

    • Hi Clark, the shop towel is on our to test list, and we will publish the result as soon as it comes out. Stay tuned!

  10. Your info about filters has been very reassuring due to the ongoing Corona Virus epidemic. The big question Ive see all over the internet and YouTube is whether or not the .3 filtering will actually work for the virus which is less than .3. So your info really cleared that up, thank you. However, these filters are filtering particles that are free floating in the air, allowing the Diffusion process to work. But, the Corona Virus more than likely is attached to droplets of saliva, so how does that change how the filtering of less than .3 will work? Im assuming our saliva is greater than .3 so in theory it should filter it, but now we have a wetness factor. Will the filter still filter the virus or will the saliva droplet be absorbed into the material causing a pathway for us to infect us? Thanks.

    • Good question Stephanie. The water droplets are bigger than 0.3 microns, meaning the HEPA filter will do an even better job of capturing these. Even if the water were to evaporate, the fact that HEPA filters can capture the tiny coronavirus has us covered.

  11. Hi! I’m wondering if you have plans to extend (more affordable) shipping of your product to Singapore? I was keen to order a blast mini, but found out shipping was basically 1420RMB – basically the same price as the product itself! We badly need great air purifiers in Singapore too, as we suffer from horrible haze conditions every year.

  12. A very interesting article Mr Robertson. I have an old Hepa filter which I was going to press into service not knowing if it would prove effective or not. Your point about particle size, specifically that of the Corona virus and the phenomena of diffusion is really interesting. Of course in an ideal world such information should have been collated by those in Government charged with the job of formulating disease control methodology. Of course nothing in life is either smoothly linear or fixed in stone but rather an ongoing process of learning like a bookshelf with only a bookend at one end and open at the other as if to invite further additions. If your article reflects accepted doctrine and is widely disseminated then perhaps it should have been placed in the public’s grasp by the Government for the purpose of public protection? If this is the case then my suspicion that the government is being either negligent, or is being partial with the truth in pursuit of some other coded reasoning still stands.
    Whatever the reality, I shall use my air filter now with renewed enthusiasm. It may not be the proverbial Bazooka to stop a tank that you have given me but even if it is a shade of that, along with the machines soft purr I will feel a touch less anxious. I’ll check out the science meantime. Many thanks for piquing my interest.

  13. Why isn’t this highlighted by the CDC as a prevention for businesses and homes? No need to select heat or cool, just select fan and leave it on. Or open windows and let air ventilate through the building and out.

    • I noticed that in underdeveloped countries, the coronavirus infection rates are about 100 times lower. One thing that is common to these countries is open windows and for the majority of shops, grocers, drugstores and others, no doors or windows. They are like farmer markets. The remaining infection sources are probably a few air-conditioned buses and trains and social distancing very difficult to practice and lack of tap water for washing hands. I think CDC has not noticed this and experts keep parroting their stance that 6 feet distance and handwashing are good enough.

  14. I run my own medical clinic in Ca and in anticipation of Corona virus I bought hepa filtration devices for each room w UV light. I know for sure the UV will kill the virus and was also happy to see your article supporting that the filters themselves are useful against viruses. Any recommendations of what filters to use for the vents. I was going to put hepa filters over those as well. I’m in a medical office w closed ventilation system. I will also be using UV to sterilized staff Ppe as we only have limited supply

    • Hello Laura,
      Which Company Filters are you using and what type of UV light ,
      I am a dentist and looking to buy theses for my office
      Thanks a lot

  15. Hi Paddy, I use Airfree at home, 24/7, an air purifier that doesn’t use filters, just purifies air by contact with an heated ceramic core at ~200ºC, thus, all airborne contaminants, including viruses, are destroyed by heat, no problems with filter clogging or any other maintenance

  16. One of the negative ion filtration products claims to trap particles as small as 0.01 microns. Do they offer equal or better virus filtration?

  17. Aloha Paddy,
    I was wondering if using filters for air conditioning systems (cutting them into squares) and placing them inside of masks that are not N95 or N99 be efficient?

    • If you’re unable to purchase masks (if they’re sold out) then DIYing masks might have some benefit. Some researchers think that one big benefit of masks is that they reduce your hand to mouth contact, potentially reducing the chances of infection. As for whether filters from air conditioning systems are good to use – I’m unclear as to what the material is, so I can’t give you a definite answer. However I would make sure that the material is safe for contact with skin (some filters can be made with fiberglass, which can irritate the skin).

      Stay tuned, we’ll have a post on DIYing your own mask to protect against Covid-19 out soon!

        • Great reference Jen! We’ll have a post about homemade mask materials online very soon. There is also this study done on homemade masks at Cambridge university, which gives a list of the most effective materials. We will be referencing this in our writeup!

  18. I need your help please. On Monday just 2 days ago..I recently purchased OxyBreath pro face masks. Does it offer any protection against the coronavirus at large? Also they said it can be washed to clean it. Will this help? After washing, is it helpful to continue using it? If the smallest coronavirus is 0.1 microns..wld it help? I would really appreciate some help. Thank you very much.

    • Hi Susana, we’ve not tested the OxyBreath pro mask, so have no way of knowing how well it filters out the coronavirus. What I suggest you do is contact the company and ask for any certifications they have for the material they use. You’ll want to ask if they use N95 or N99 type materials, and ask to see the certifications. The 3M masks we tested use N95 and N99 materials, and were able to capture over 95% of virus-sized particles. If the mask is using one of these materials then it’ll likely be filtering out the coronavirus as well.

      Breathe safe!

      • Hi Paddy. Interesting website and test results. So if one were to buy the N95/99 masks from 3M can they be used for a long period of time or are they single use? If the virus ends up rife where I am, I couldn’t afford to be replacing them each day I’m afraid so any advice about longer term use would be appreciated. Thank you very much.
        Best wishes,

        • Hey Rich, great question! I’ve been hearing this a lot lately – we have a shortage of masks, so can we use them for a longer period of time? In terms of the ability for the mask to capture those tiny particles: our data shows that the masks are just as good even after 10 days of use. However, that doesn’t take into account whether or not the mask becomes contaminated with the virus. If you wanted to use them for extended periods of time, then you’d likely need to disinfect them if you’re worried about them becoming contaminated. We’re in the process of running some tests to see whether disinfecting affects the mask’s ability to filter tiny particles. Preliminary results (you heard it hear first!) show that washing masks with water damages the mask fibers beyond repair. Washing with an alcohol wipe may have some benefit – we’re working on a write up for this now, so stay tuned!

        • Hey Paddy. I’ll be following your site to see what your test results are. What about other methods of decontamination eg UV immersion?

        • Thanks for getting back to me. This is a very important discussion and the research you are doing is invaluable.

        • How about simply spraying the mask with alcohol? I’ve been doing this after going outside shopping with each item purchased.

        • We’re in the process of testing this Ben. Our expectation is that it won’t reduce the masks ability to capture nano-particles much (if at all). However the tough question is: can spraying your mask really kill all the viruses on the masks? Stay tuned for an update on this post.

        • Hi Paddy. When can we expect an update on cleaning options, please mate? I’m thinking about 3M disposable face masks which are quite cheap, but they would soon be very expensive if I had to replace every day.
          Cheers and best wishes, Rich

        • But in theory, shouldn’t the virus self-eliminate (die) within 3+ days (or to be more safe, after 7 days or so)? So cannot one leave the mask just as it is, in a remote place, and then pick it up and re-use it?

          Or, what would happen when putting the used mask into a hermetically sealed glass/mason jar, together with oxygen absorber, would the virus(es) die?

        • You’re smart Lissy! That’s exactly right. Our current best recommendation for cleaning/disinfecting masks is for people to leave them in a dry place for 12+ hours. Data shows most viruses die (or are no longer ‘viable’ to use the technical term) after being on cloth-like material for over 4 hours. That means masks and other similar materials are likely to be virus-free after leaving them for just 4+ hours!

        • Hi Paddy, thanks for all your excellent advise. If people leave used masks on a cloth-like material in a dry room in the house ( a room that is not usually used for example) would there be a risk that the air in that room would become contaminated? Once one puts the used masks on a cloth – like material where do you recommend we leave them? Thank you. All the best.

        • Good question Maria, can the viruses come back out of the filter/mask? A group or researchers tested wether plutonium particles (0.3 microns in size) were released from HEPA filters when they were repeatedly tested under “mechanical shock flow by free fall from a height of 50 mm every half minute.”

          They found very little indication of the particles coming out of the filter. From this, we can assume that leaving a mask or filter inside our house, it’s very unlikely to release virus particles back into the air. I’d suggest you leave your mask in a dry place, out of the way so you don’t touch or move it.

        • If the elastic fasteners are detached (and later replaced), can the masks be microwaved for x seconds? The metal in the nose part will not be a problem in the microwave if the unit is in a bowl covered by a silicon microwave food cover.

        • Or maybe heat? We’d need to know how high a temperature the mask can take without harm, and the temperature needed to denature a specific virus (which might vary with moisture/dampness).

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