How to Clean Air Purifier HEPA Filters and Are They Washable?

Can you clean a HEPA filter? If so, how should you wash or clean a air purifier 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 cleaning them isn’t ideal. It would be great if we can clean and wash and re-use HEPA filters.

Some ‘Experts’ Say You Can Clean 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, cleaning, and vacuuming HEPA filters in the Smart Air lab.

Smart Air engineer CK testing washing and cleaning HEPA filters

When you search for “how to clean HEPA filter,” you will see two methods to clean HEPA filters: vacuuming and washing.  Smart Air put both of these to the test.

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 traveling 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 it 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.

Read More: How to Know When to Change My HEPA Filter?

Bottom Line: How to Clean and Wash a HEPA Filter?

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

Therefore, 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.

Smart Air

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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