Premier One Annual Filter Replacement Kit Contains 3 Pre-Filters And 2 Carbon Filters Pre-filter Size 16x13.5x1 Carbon Filter 15.75 x 15 x .58 HEPA

HEPA (High Efficiency Particulate Arrestance) filters are used in hospitals because they are considered the best filters on the market today. Originally developed by the Atomic Energy Commission during World War II to remove radioactive dust which was invisible, but health hazardous, from manufacturing plant exhausts. A filter must collect 99.97% of a specific particulate that measures 0.30 microns, in a test established by the Institute of Environmental Sciences in order to receive the HEPA filter designation. However, the HEPA filter can capture 100% of all particulate sizes ranging from , 100 microns down to 0.01 microns. The HEPA media is made of very thin glass fibers. They are made into paper much the same way as cellulose or wood fibers are used to make paper. In texture it is very much like blotting paper and air cannot pass easily through this dense mass. A large area of paper must be used to permit the filtration of a large volume of air. To get the large area it is pleated: hence the term: extended surface.