Here's what you need to know.

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If there is one thing we've had serious second thoughts about over the last year, it's the quality of the air we breathe. From COVID-19 airborne particles and droplets, to raging wildfires sending air pollution and smog across the country, protecting your air quality (and your lungs) is important. Many folks have been investing in HEPA air filters to improve the quality of the air they breathe at home. Below, we asked two experts for their thoughts on HEPA filters—how they work, how to clean them, and how often to replace them, too. 

Air purifier
Credit: Getty Images

What is a HEPA filter? 

A High Efficiency Particulate Arrestance (HEPA) filter provides the highest filtering efficiency of any air filter. A HEPA filter must meet a specification set by the United States Department of Energy and be capable of filtering at least 99.97% of particles sized 0.3 microns (one millionth of a meter). "Interestingly, due to how these filters remove particles, the size 0.3 microns is the hardest size to capture," explains Ted Myatt, ScD, a senior environmental scientist at Environmental Health and Engineering, Inc. "They actually remove even a greater percentage of particles both larger and smaller than 0.3 microns."

A HEPA filter is different from a normal air filter in a couple of ways. First, it is made of a filter material that is sheets or mats of randomly arranged fibers (e.g., fiberglass), according to Myatt. These sheets look similar to rough paper, and the randomness of the fibers creates narrow pathways for air to pass. Then the sheets are heavily pleated so there is a large surface area for the particles to pass through.

According to John Bloemer, an executive advisor and engineering fellow at Aprilaire, a typical air filter might be something like the MERV (Minimum Efficiency Reporting Values) 8 filter, which is a 1" filter you may find in a typical air handler or at your local retail store. "A MERV 8 filter, by definition, does not have to have any particulate filtration efficiency (0% effective) on 0.3" microns," says Bloemer.

How to clean a HEPA filter

Unfortunately, you can't actually clean a true HEPA filter—it must be replaced. "Water would likely damage the sheets of fibers and would remain trapped in the pleats," explains Myatt. "In many cases, manufacturer's sell products like "HEPA-like" filters that can be cleaned—these filters are not true HEPA filters and will likely have slightly lower efficiency at removing particles."

True HEPA filters used in portable air purifiers or whole home ventilation systems are easily replaced, as opposed to cleaned. "Typically, it can be as easy as popping it out and replacing it with a new filter," says Myatt. While you shouldn't be concerned that the material trapped on the filter will be released when removing, Myatt suggests doing it it carefully. For example, you could consider wearing a mask and make sure to have a trash bag ready to place the old filter into. Always follow the manufacturer's instructions for this process. 

It's important to note that trapped materials like SARS-CoV-2 will very likely no longer be infectious after being trapped on the filter. "But mold and allergens will still remain a concern if the individual replacing the filter was allergic to those materials," warns Myatt.  

When should you replace a HEPA filter?

HEPA filters can typically last six months or longer, depending on how often they are used and how dirty the air is. "Some products, like the Honeywell Insight Portable Air Purifier, have systems designed to tell you when a filter needs to be replaced," explains Myatt.

Although MERV 8 filters may not filter out a ton of fine particles in the air, the MERV 13 and MERV 16 filters can remove between 50-95% of air particles, according to Bloemer. "The other thing to remember is that most 'HEPA' filters available to the residential customer are in portable air cleaners and are designed to clean only one room of a home," he says. "A good quality MERV 13 or 16 filter in your HVAC system will clean your whole home—make sure to contact a local HVAC contractor and go with a reputable filter manufacturer."