What Is a HEPA Filter?
HEPA, which stands for high-efficiency particulate air, is a type of air filter that basically looks like folded paper. If you have a quality portable air purifier in your home, it likely has a HEPA filter, which is a filter consisting of an interwoven matrix of fibers for air to pass through. Because the fibers are densely packed, they create a very small pathway for air to travel through. This net of fibers captures small particulates and filters them out of the air you breathe, says George Negron, vice president of operations at air quality company EnviroKlenz, which ultimately helps improve indoor air quality. HEPA filters may also be found in your home’s air handling system, and some vacuum cleaners have them, as well.
What Do HEPA Filters Do?
Filters are defined by how efficient they are at removing particulates from an air stream. HEPA filters are very good at capturing particles of all sizes and theoretically remove at least 99.97 percent of particles with a size of 0.3 microns. These are among the most difficult particle sizes to catch, says John Bloemer, an engineering fellow at Aprilaire who’s been in the air quality industry for more than two decades.
HEPA filters collect harmful microscopic particles.
These 0.3-micron particles come from things like combustion smoke, smog, and diesel exhaust, and because of their size, they can go deep into your lungs as you breathe, Bloemer says. By contrast, particles such as the pollen that aggravates your allergies each spring are typically 10 microns, so they’re captured by your body’s own filtration system (i.e., your nose and throat) rather than going into your lungs. That’s why HEPA filtration is so critical to capturing those 0.3-micron particles.
Can You Clean a HEPA Filter?
If you see a visible buildup of dust or particles on a HEPA filter (it may look gray or dirty) or observe reduced airflow through your portable air purifier, you may assume that’s an indication the HEPA filter needs cleaning. However, experts say HEPA filters should always be replaced rather than cleaned.
Cleaning destroys the filter.
“You cannot clean a HEPA filter by using something like a vacuum because the particles are trapped not only on the surface of the filter but also deep inside the media,” Bloemer says. Don’t even think about running it under your sink, either—liquids like water and soap will destroy the filter media, he adds.
Some caked-on dirt is OK.
When you’re seeing buildup on a HEPA filter, that’s all the captured particles, which can range from particles generated from combustion (think car exhaust, gas stoves, and candles) to mold spores and animal dander, says Ted Myatt, ScD, senior scientist at Environmental Health & Engineering. These particles can be generated indoors or outdoors and migrated through open windows, wall joints, or cracks. It may sound counterintuitive, but on one level, a HEPA filter may work better when it has a thin, caked-on layer of collected particles—but at some point, air will have a hard time getting through the filter, Myatt says, which means the filter needs to be replaced.
Pre-filters can be cleaned.
The one 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. This pre-filter will capture some of the larger dust and particles, and some of these prefilters are washable to enable you to remove the dust and debris they collect—note that this is not the actual HEPA filter, though. Again, experts agree that HEPA filters should always be replaced when dirty and not cleaned.
How Do You Replace a HEPA Filter?
If you observe that your HEPA filter has a visible buildup, the best plan of action is to purchase a new filter. To do this, turn off your unit, find the access door, remove the old filter, and put the new one in, Bloemer says. You don’t have to leave it up to your own eyes, though. Most manufacturers will also provide a recommended changing interval (which generally is around six to 12 months), and some portable air purifiers will have an indicator light that lets you know when to replace the HEPA filter. However, time is not always the best indicator, says Negron, since the true reason to replace a HEPA filter is based on how much particulate matter is collected, which can vary widely in different environments. If your air purifier is constantly running or your space is particularly smoky or pollen-filled, plan to replace your HEPA filter more often.
