Can You Clean or Wash HEPA filters?

Can you wash a HEPA filter? If so, how should you wash or clean a HEPA filter?

These questions keep cropping up, as they’re just about the  only remaining problem for HEPA filters.

HEPA filters are almost perfect: they are backed by tons of scientific tests; they’re pretty cheap; they use about as much energy as a lightbulb; and they even have documented health benefits. But replacing them as opposed to washing them isn’t ideal. It would be great if we can wash and re-use HEPA filters.

Some ‘Experts’ Say You Can Wash HEPA Filters

On the question-answer site Quora, I’ve seen industry insiders say you can clean HEPA filters by banging the HEPA filter to get the dust out:

 

Expert explains you can clean a HEPA filter by banging out dust

 

Some people even say you can clean HEPA filters by vacuuming them:

 

Suggestions that we should use a vacuum cleaner to clean a HEPA filter

 

…or even by washing HEPA filters with water. Yet other experts say you can NEVER clean HEPA filters.

HEPA filters should not be washed but replaced

 

But one thing I haven’t seen is anyone actually test the question and present the data. To get to the bottom of whether we should clean HEPA filters, and the best way to clean them, Smart Air engineer CK tested washing and cleaning HEPA filters in the Smart Air lab.

Smart Air engineer CK testing washing and cleaning HEPA filters

 

1. Cleaning HEPA filters by Vacuuming

The first test we tried was vacuuming HEPA filters. We took a dirty HEPA filter, ran tests on its performance before cleaning, vacuumed it, and then ran more performance tests after cleaning it. In all, 8 dirty HEPAs which had been used for 3-4 months in Beijing air were tested.

vacuuming HEPA filters to remove clogged dirt and reuse them

 

Testing Effectiveness of Vacuumed HEPA Filters

For each cleaning method, CK ran 3 types of tests to measure the performance increase or decrease in the HEPA filter before and after cleaning. CK tested:

  1. Particle Capture: To see how cleaning the HEPA filter impacted capture performance, the percentage of 0.3 micron particles by the HEPA was measured before and after cleaning. 0.3 micron particles are a great benchmark because they are the hardest particle size for HEPAs to capture.
  2. Air Flow: The amount of air travelling through the HEPA filter before and after cleaning can tell us if the HEPA filter is less clogged, or if the fibers in the HEPA filter have been damaged due to washing.
  3. CADR: CADR is the ‘gold standard’ for measuring an air purifier’s performance. It measured the total combined impact (particle capture + air flow) of washing on the HEPA filter

 

Here’s how the 8 HEPA filters that were vacuumed performed before and after cleaning:

Effects of vacuuming HEPA filter on its performance and clean efficiency

 

Should You Vacuum HEPA Filters: Results

On average, vacuuming increased CADR by about 10%. But there was also a lot of variance, ranging from a 14% increase to a 3% decrease. Based on that data, cleaning a HEPA by vacuuming might help a little, but there’s also a decent chance it’ll do nothing at all, or could even damage your filter.

 

What’s The Vacuum Doing to the HEPA Filter?

HEPAs are made of thin fibers. The vacuum is probably pulling out some of the larger dust particles from the HEPA filter, but at the same time some of these fibers as well. You can see what looks like fibers that have been pulled loose in this picture.

 

vacuuming HEPA filter can remove clogged dust particles but also damage fibers

 

Vacuuming bottom line: There may be a slight benefit of vacuuming HEPAs, but the benefit is small, and it can also damage the HEPA. Therefore, we do not recommend vacuuming.


2. Cleaning HEPA filters by Washing With Water

Vacuuming did very little to improve the HEPA filters’ effectiveness. So, how about washing HEPA filters instead? This time, CK tested 3 HEPA filters by washing them under a shower head (with water only) and then leaving them to dry for a day.

How NOT to wash HEPA filters with water

 

Should You Wash HEPA Filters With Water: Results

I stopped testing after 3 trials because the results were so conclusive: washing HEPA filters with water decreased effectiveness by an average of 32%.

 

HEPA filter performance decreased greatly after washing with water

 

Why Is It Bad to Wash HEPA Filters?

To get to the bottom of why washing was so bad for the HEPAs, I looked at wind speed and particle capture before and after washing.

First, washing actually increased the amount of air passing through the HEPA filter.

Washing a HEPA filter can improve the airflow through the filter, but may still damage or destroy the HEPA filter

Great, right!? But then the particle capture of the HEPA filter actually went down a lot after washing.

 

The number of particles captured by the HEPA filter after washing dropped drastically due to the water damaging the filter

Washing the HEPA filters probably broke some of the fibers or made the gaps between the fibers larger. That would explain why more air passed through after washing, but also more particles!

Washing bottom line: Washing HEPA filters with water significantly decreases performance you should not wash a HEPA filter.


Bottom Line: Can HEPA Filters be Cleaned or Washed?

Vacuuming HEPAs may improve performance, but the effect is small. Washing HEPAs strongly decreases performance. We do not recommend washing HEPAs.

As such, HEPA filters should still be replaced when it starts to get clogged and its effectiveness dropped. When is this? Learn why the standard numbers might not always be accurate.

 

 


Washing & Cleaning HEPA Filters: Open Data

You can learn more about the testing methods and view the original data in the supplemental data article.


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Leiko Washington

On the masks with hepa filter I use a UV sterilizer and after a while just throw out the mask filter and stick in another one. I use pieces of the filtrate in a mask with a filter pocket. The UV sterilizer is on Amazon

Linda K Carter

I’ve been taking apart Filtrete Elite Allergen filters to use in face masks I make given the unavailability of adequate masks for us common folk. I’d been blasting the masks with my steam cleaner or steam iron and now I’ll stop with this information about a stream of water widening the airways in the filter. Another way to sterilize the filter after use would be to put it in an oven on its lowest heat, 170, or on a dryer rack at high heat setting. Or leave the mask in the dashboard of your car while it sits in the… Read more »

J Larson

The CDC says you can just leave the mask unused for five days or more. Letting it dry out will probably help kill any virus on it a bit faster, they don’t like it dry. They suggest putting it in a paper bag labelled with your name. Some hospitals in the US are doing this, 5 masks per healthcare worker…
https://www.cdc.gov/coronavirus/2019-ncov/hcp/ppe-strategy/decontamination-reuse-respirators.html

J Larson

See “The Best Way to Disinfect Masks Without Destroying Them”: https://smartairfilters.com/en/blog/disinfect-clean-n95-mask-virus-coronavirus/

Sherwood Botsford

Hmm. What causes a filter to lose effectivness? My intuition says that the spaces between the fibers get plugged with particles. What about this: Wash a HEPA filter. Now has decreased drag and decreased capture. But is is now usable as a pre-filter for the new filter, and would it extend the new filter’s life. Other places where you use this strategy: My pond water filtration has a coarse screen on the inlet to keep from sucking in weeds. Then a sand filter, then a 400 micron screen filter then a 70 micron disk filter. Each can be back flushed.… Read more »

This is pretty much the exact same mechanism with HEPA filters. After use, they get clogged, reducing the airflow. However, if you clean your HEPA filter you may well damage the fibers so much that it ends up not being able to capture many particles. Our data on washing HEPA filters with water above shows this.

Cynthia Lemmon

What about using pre filters over them for catching larger particles then washing pre filters

This is the exact purpose of a pre-filter! They are smaller filters designed to catch the larger particles, which can then be washed or replaced more easily. It helps prolong the lifespan of the HEPA filter, but capturing most of the large particles and stopping the HEPA filter from getting clogged.

amoghdutt

Hello! Is it possible to use a blower to clean HEPA filters, at least superficially? To be specific, I’ve been using the Sqair for only a little over a month, but there’s already a significant amount of dust (and dust bunnies?) in the filter (I don’t use a pre-filter). I was wondering if such visible amounts of dust affect cleaning performance. My hunch is that blowing the filter would also damage it–would that be correct?

Liz - Smart Air

Hi Amogh, if you read the article, we tried to vacuum the HEPA filter. I guess blowing it would be about the same effect. Some dust can get out, but the CADR will not increase dramatically. Here is a test we did or the HEPA lifespan, it tells how the HEPA efficiency changes as time passes: https://smartairfilters.com/en/blog/sqair-hepa-lifespan-test/ I don’t suggest to clean the HEPA filter, if you live in a place with heavy dust, cover the grill on top with a clean and dry cloth when you don’t use it. And when you use it, since the air is blowing… Read more »