HEPA filters are commonly used in air purification systems or vacuums to trap dirt, dust, impurities, and allergens in the air. Cleaning the filter and removing build-up can restore the life of the filter and allow it to be reused. Permanent or washable HEPA filters can be cleaned and reused several times, as long as it is done correctly without damaging the filter. Most permanent HEPA filters can be cleaned gently with a vacuum, while washable HEPA filters can be cleaned by rinsing it with cold water. If you're not sure if the HEPA filter can be cleaned, look for the “washable” or “permanent” label on the air purifier's packaging, box, or website.
However, you should do it as carefully as possible to avoid damaging it. There are no officially defined standards or terms as to what type is considered permanent or washable. If the filter is marketed as washable or permanent, then you may be able to wash or clean it and it will continue to work. However, there is no standard for washable HEPA filters and there have been no public studies to test how well these filters work after washing. To clean the HEPA filter, you must use a strong stream of cold water and not use detergents or other chemicals. The glass threads of the fibrous filter are entangled and compressed in countless directions to form a filter mat less than 1 micron in diameter. Trying to clean a HEPA filter usually doesn't do anything to improve the filter's performance, and washing it will open holes that will actually worsen its performance.
There are a lot of reasons why most HEPA filters can't be washed, as improper cleaning can be a bad idea. HEPA stands for high-efficiency particulate air and is a type of mechanical filter that traps 99.97% of harmful particles in the air as small as 0.3 microns (0.00001 inch, 0.0003 mm). You must dry the filter thoroughly, as leaving it moist will allow microorganisms and bacteria to grow and spread in the filter. Air purifier replacements are expensive and it's incredibly annoying to try to keep them stocked in your home. If you have a quality portable air purifier in your home, you probably have a HEPA filter, which is a filter that consists of an interwoven matrix of fibers through which air passes. Combine that with the fact that you may end up cleaning the reusable filter very frequently, and it's clear that these devices aren't a hit compared to their non-reusable competitors. If you buy an air purifier, like the one I recommend (the BlueAir-211+, which I've reviewed here), you'll know that the ongoing expense of replacing filters can be high. If you notice that your HEPA filter has a visible build-up, the best plan of action is to buy a new filter, turn off the unit, find the access door, remove the old filter and place the new one, Bloemer says.
The only exception to replacing a HEPA filter when it's dirty is if you have an air system that has a pre-filter in front of the HEPA filter, Negron says. Most manufacturers also offer a recommended replacement interval (which is generally about six to 12 months), and some portable air purifiers have an indicator light that tells you when to replace the HEPA filter. You can also find HEPA filters in many appliances, including air purifiers, vacuums, air conditioning systems, and cars.