How Do HEPA Filters Work?

How Do HEPA Filters Work?

Learn how a HEPA filter purifies air and protects your family

By Stevie Donald

Close-up of HEPA filter
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High-efficiency particulate air filters remove almost 100 percent of particulates from the air, even microscopically tiny particles from cigarette smoke, pet dander, mold and even some viruses, according to the Environmental Protection Agency. Improving indoor air quality is critical to managing asthma and respiratory diseases. HEPA filters use highly absorbent material to trap the particulates.


HEPA filters are used to clean indoor air in commercial and residential buildings when installed in the heating and cooling system. This is not always practical for homes, however, because installing HEPA filters in the existing ductwork may require extensive restructuring of the ducts. HEPA filters also are available in portable, single-room air cleaners and vacuums. People working with dangerous substances, such as lead and asbestos, wear masks equipped with HEPA filters to prevent inhalation of dangerous dust or fibers.


Whether large enough for a building or small enough to fit in a protective face mask, HEPA filters work the same way. Fiberglass is used as the filtering material, and is folded and pleated tightly so that a large surface area is compressed into a relatively small space. As the air passes through, particles as small as 0.3 micrometers lodge in the filter.


HEPA filters are used in medical facilities and hospitals to reduce airborne bacteria and some viruses. They also are used in airplanes, some commercial buildings, and any industrial application that produces potentially harmful particulates in the manufacturing process. Smaller filters are available for vacuum cleaners, masks and portable air cleaners. Some filters are washable, but most are not and should be changed annually. Because replacement HEPA filters can be expensive, research your indoor air quality options carefully.


HEPA filters were developed in the 1940s to prevent radioactive particles from escaping from nuclear plants. Since then, they have been in wide use in military, medical and industrial settings.They have been commercially available for private use since the 1950s.


According to the EPA, HEPA filters do not completely remove all the particulates from the air because many larger particles settle quickly on indoor surfaces. A Johns Hopkins University study showed little effect of HEPA filters on allergic people who shared their home with cats and Consumer Reports gives them mixed reviews for efficiency. The EPA states that less-expensive, medium-efficiency pleated filters are likely to be just as effective as HEPA filters in the home and in some cases may perform better.

About the Author

Stevie Donald is a regular contributor to DexKnows. She has been a painting contractor since 1979.

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