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:
Some people even say you can clean HEPA filters by vacuuming them:
…or even by washing HEPA filters with water. Yet other experts say you can NEVER clean HEPA filters.
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.
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.
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:
- 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.
- 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.
- 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:
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 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.
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%.
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.
Great, right!? But then the particle capture of the HEPA filter actually went down a lot after washing.
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.
Washing & Cleaning HEPA Filters: Open Data
You can learn more about the testing methods and view the original data in the supplemental data article.