Can You Clean or Wash HEPA filters?

HEPA filters are a nearly perfect solution for air pollution. They are backed by tons of scientific tests; they’re pretty cheap; they use about as much energy as a lightbulb; they even have documented health benefits.

Just about the only remaining problem is that you have to throw out the HEPA filters every few months. Can you wash a HEPA filter? If so, that’d be great because we could re-use. Here put to the test whether you can clean HEPA filters.

 

People have lots of opinions! On the question-answer site Quora, I’ve seen people say you can clean HEPA filters by banging the HEPA to get the dust out:

 

clean a HEPA filter by banging out the dust

 

…or to clean a HEPA filter vacuuming it

 

clean a HEPA filter by vacuuming

 

…or even wash it. Then I’ve seen other people say you can NEVER wash a HEPA.

 

you can never clean a HEPA filter

 

But one thing I haven’t seen is anyone actually test the question. Well now I’ve got data. That’s because CK from Smart Air decided to test out the best way to clean a HEPA filter. Here’s CK’s story.

 

 

Vacuuming the HEPA

First I tried vacuuming a HEPA. I took a dirty HEPA filter, ran tests on its performance, vacuumed it, and then ran more performance tests. In all, I tested 8 dirty HEPAs given to us by avid Smart Air users! They all used in China for between 2-4 months.

 

Testing Effectiveness

Particle Capture: I measured the percent of 0.3 micron particles captured at the outlet of the HEPA before and after washing. 0.3 micron particles are a great benchmark because they are the hardest particle size for HEPAs to capture.

Air Flow: I measured air speed coming out of the HEPA before and after washing.

CADR: I used particle capture and air flow to estimate CADR.

 

 

Vacuum Results

On average, vacuuming increased relative 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, I’d say cleaning a HEPA by vacuuming it might help a little, but there’s also a decent chance it’ll do nothing at all.

 

What’s The Vacuum Doing?

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.

 

HEPA

 

In short: 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.


Washing the HEPA filter

So, what if we wash them instead? I used the same 3 filters that were vacuumed before and washed them under a shower head. Then I gave them a day to dry.

 

 

Results – Washing your HEPA filter

I stopped testing after 3 trials because the results were so conclusive: cleaning the HEPA through decreased effectiveness by an average of 32%.

 

 

Why Was Washing So Bad for the HEPAs?

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 the HEPA.

First, washing actually increased the windspeed.

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

 

effectiveness of HEPA filter after washing

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

In short: Washing HEPAs with water breaks down the HEPA material and so is not recommended.


Bottom Line – can you wash HEPA filters?

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

Based on this data, it seems it really is not possible to clean your HEPA filter – either by washing your HEPA filter or vacuuming your HEPA filter. We still recommend replacing your HEPA when its effectiveness drops. When is this? We tested this with the Smart Air DIY air purifier found replacing after 140 days is best. For the larger HEPAs, like those in the Blast and Blast Mini purifiers the huge surface area means they can last over 1 year.

Own another purifier? Learn why the standard numbers might not always be accurate.

Open Data

You can learn more about the testing methods, and view the original data in the Supplemental Data article. Click here to learn more.

 

The Sqair air purifier Kickstarter

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David Glatz

I work at a humane society, and we have Hepa filters mounted in ceiling in our surgery suites. I have read some articles about cleaning them, washing them with water will damage them i believe. Vacuuming them doesnt seem that would clean them thourgh enough. The filters i need to replace are very costly, any sugestions on how to clean? Trying to avoid replacing due to cost, but i may have to. If i have to replace with new ones, how often would you sugest?

Hey David! I’ve been researching washable and/or re-useable HEPA filters for 4 years and unfortunately have yet to see any viable solutions to this. Right now the only really viable option is to replace them. You could consider putting washable pre-filters before your HEPA filters (they are coarse, thick filters which can capture dust and larger particles, hence extending the lifespan of your HEPA filter) but you will need to check that your system can handle the extra workload caused by pushing air through an extra filter. Having said all this, HEPA filter technology was invented over 70 years ago,… Read more »

Rob

I vacuumed my Kenmore 85150 PlasmaWave AirCleaner’s hepafilter and carbon filter. They looked pretty good after, without the obvious loose fibers that you show in the image above. Can’t say that some particles haven’t been disturbed. More importantly, though, I reset the “change filter” light – it went off right away and hasn’t returned for more than an hour. It seems that the machine would know if the filters are doing the job. What do you think?

Hey Rob, interesting you’ve tried this on your Kenmore! That’s a good question on the ‘change filter’ light. I can’t speak for the Kenmore you have, but most ‘change filter’ functions work on a simple timer basis. The timer counts down from a fixed number of hours, then the light comes after exceeding this time. What this means is that when you reset the light, it normally just resets the timer. I’d say that unless you have an air quality monitor, it will be very difficult to know if it’s improved the filtering efficiency of the Kenmore or not.

Lukas

It would be interesting to wash the HEPAs in non-water liquid. Ethanol or Isopropyl alcohol instead. Or even use some chemicals (Tetrachloroethylene…) they use in dry-clenaning where they wash suits and other stuff you just can’t put in washing machine. I am really a novice in “clean air technology” but I once washed my Roomba’s old hepa-style filter in water and it became soft etc (well it was wet – no surprise. And this probably made some changes you described in this article ). But when I tried to was it in Isopropyl alcohol the filter remained rigid like it… Read more »

Wallis

Really appreciate this post – thanks!

Somewhat Reticent

Since these filters trap particles, I wonder why you did not include testing for vibration during reversed fan direction?
You mention “banging” – did you test vibration at all, to first dislodge particles?
If you’re not comfortable using a massage vibrator, perhaps tapping with drumsticks while aiming downward?
If compressed air or vacuuming is too violent, what of simply reversing direction and using the same fan?