HEPA is the abbreviation for "High Efficiency Particulate Arrestor {Air filter}."  HEPA  is not a brand of air cleaner. It is a type of air filter that is used in air cleaning equipment including vacuum cleaners. Most HEPA air cleaners will filter particles in the airborne environment down to 0.3 microns in size, at an efficiency rating of 99.97%. They will filter and remove some of the smallest microns of allergens such as dust, smoke, pollen, animal dander , etc. When companies remove asbestos in buildings, and clean up pharmaceutical and other potentially toxic spills, the HEPA filtered air cleaners and vacuum cleaning equipment are the required tools for the job. These air cleaners work by filtering the particulate (allergens) in the air through a HEPA filter which traps the particles, allowing only the clean air to return into the environment. The more times the air is exchanged through the HEPA air cleaner in the room , the better the air quality.  The higher the air exchange rate per hour, the cleaner the air will be in that room. HEPA air cleaners will most efficiently service one room at a time. If you operate the HEPA air cleaner in your bedroom, it will not be able to clean the air in your living room or in other areas of your home. The better brands of HEPA air cleaners such as Austin Air and Clarifier will provide approximately 15 air exchanges per hour in an average size bedroom and approximately 5 to 7 air exchanges per hour in a 1500 square foot open room. The average department store quality HEPA air cleaners will only provide approximately 2 to 4 air exchanges per hour in a average size bedroom. In a larger size room, these lower quality brands of air cleaners will not often provide a high enough air exchange rate to make a noticeable difference in your indoor air quality. The higher quality HEPA air cleaners also contain an average of 15 lbs. of activated coconut carbon / Zeolite blends to absorb offgasing chemicals and odors. Some high quality HEPA  air cleaners ,also have the added feature of a medical grade ultra-violet light system. The ultra-violet lights will quickly kill viruses, bacteria and fungi when the contaminated air enters into the HEPA air cleaner. The ultraviolet-light will also protect the HEPA filter itself from biological and virus contamination. The lower quality brands HEPA air cleaners on the market, contain pre- filters that have been sprayed with carbon dust which is extremely short lived and more of a sales gimmick than a viable way of removing odors and offgasing chemicals.