HEPA filters are a type of mechanical air filter known as a high-efficiency particulate air filter, developed by the Department of Energy (DOE) following the Manhattan Project in the 1940s. They are designed to trap particles in the air, such as dust, pollen, mold, bacteria and any particles with a size of 0.3 microns (µm) or larger. HEPA filters are highly effective at removing large particles such as pet dander, pollen and dust mites, and are recommended to minimize these common household allergens. However, just because a filter or vacuum bag says HEPA doesn't mean you're getting true HEPA performance.
ULPA filters trap more and smaller particles than HEPA filters, with 99.999% efficiency at removing submicron particles 0.12 microns in diameter or greater, while HEPA filters are 99.97% efficient at removing particles 0.3 microns in diameter or larger. To maximize the effectiveness of a HEPA filter, it is recommended to combine it with pre-filters to trap larger particles before they come into contact with the main filter. When used in both air purifiers and vacuum cleaners, HEPA filters offer the best chance of cleaning indoor air. However, other measures such as keeping windows closed, having no indoor plants and washing curtains regularly are also necessary to reduce the amount of airborne pollutants in a home. Manufacturers of high-quality HEPA filters voluntarily test and certify their filters to meet DOE standards, labeling them as “absolute HEPA” or “true HEPA”. It is important to note that while a HEPA filter can help improve indoor air quality, it should not be assumed that an air purifier equipped with a HEPA filter will fully protect from infection. Because dense HEPA filters trap most of the particles in the air, they tend to clog more quickly than traditional filters.
It is recommended to replace them at least twice as much as non-HEPA filters. Additionally, there are many harmful contaminants in the air that are not particles and cannot be trapped by a HEPA filter. When considering buying an appliance with a built-in HEPA filter, it is important to understand what these filters can (and can't) do to help improve the air quality in your home. It is also important to consider new air cleaner technologies that destroy pollutants rather than simply trapping them like a HEPA filter.