The military designed the first HEPA filter in the 1940s for use in the Manhattan Project, when safety from free-floating nuclear material was a primary concern. Today, HEPA air purifiers are very widely used to remove dust, pollen, mold, bacteria, and other airborne particles. They are perhaps the most tried-and-true method of air cleaning to date. The best part about HEPA air purifiers is that they emit no byproducts or secondary pollutants such as ozone.

The Department of Energy continues to be the sole certifying body for all HEPA filters. The DOE has strict standards. All HEPA filters must be able to catch at least 95% of particles as small as 0.3 micrometers. If you are shopping for HEPA air purifiers, beware of HEPA-type or HEPA-like filters. They did not pass DOE muster on their ability to filter air.

HEPA Air purifiers work by drawing in air via a fan. Large particles get trapped in the folds of the filter, while small particles and chemicals attach to the charcoal matter in the filter.

Some fans have a straight design whereby the air is drawn in from the back and blown out through the front. These units clean the air very quickly and are good for aiming at your bed or sitting area.

Other fans are unidirectional, pulling in air from all sides of the machine and blowing the filtered air out in all directions. These are good for cleaning the air in whole rooms.

Related to HEPA filters are ULPA filters. ULPA means Ultra High Efficiency Particulate Air. ULPA filters are only used when there is a significant biohazard or equally harmful environment. You wont need one at home; if you do, you shouldnt be living there.

Friedrich, Oreck, and Whirlpool are some of the leaders of the industry. Their HEPA air purifiers are known for their relative quietness, air-cleaning efficacy, and energy efficiency.