What is a HEPA filter?
HEPA is a type of pleated mechanical air filter that is common in portable air cleaners, also known as air purifiers. It is an acronym for "high efficiency particulate air" filter, as officially defined by the U.S. Department of Energy. This type of air filter can theoretically remove at least 99.97% of dust, pollen, mold, bacteria, and other airborne particles with a size of 0.3 microns (µm). The diameter specification of 0.3 microns corresponds to the worst case; the most penetrating particle size (MPPS). Particles that are larger or smaller are trapped with even higher efficiency.
By contrast, Minimum Efficiency Reporting Values, or MERVs, report a filter's ability to capture larger particles between 0.3 and 10 microns.
- MERV is helpful in comparing the performance of different filters, particularly for furnace or central heating, ventilation, and air conditioning (HVAC) systems.
- The higher the MERV rating, the better the filter is at trapping specific sizes of particles.
- For more information on MERV ratings, see the "What is a MERV rating?" link below.
Review EPA’s Guide to Air Cleaners in the Home for more information, including tips on selecting a portable air cleaner, furnace filter, or HVAC filter.