HEPA Filter History and Specifications
ULPA filters, or "Ultra-HEPA" filters, are designed to trap 99.999% of all airborne particles with a size of 0.3 microns from the air that passes through the filter. These filters are sometimes used in laboratory and industrial applications such as cleanrooms.
Consumers can select air filters by looking at their efficiency in removing airborne particles from the air stream that passes through them. For an air filter installed in HVAC system ductwork, this efficiency is measured by its Minimum Efficiency Reporting Value, or "MERV." This measurement technique, developed by the American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE), allows the efficiencies of air filters supplied by different vendors to be compared.
True HEPA filters have MERV ratings between 17 and 20; high-efficiency filters have MERV ratings ranging from 14 to 16; and medium-efficiency filters have MERVs ranging from 5 to 13. Most residential HVAC systems do not have sufficient fan or motor capacity to accommodate true HEPA filters. However, according to this EPA guide to residential air cleaners, air filters with MERV ratings between 7 and 13 may be nearly as effective as true HEPA filters in filtering most indoor airborne particles.
What is a Micron?The size of airborne particles that air purifiers capture are measured in microns, which are approximately 1/25,400 inch or 100 times smaller than the diameter of a human hair. Particles 1 micron in diameter are not visible to the naked eye.
What is Microban?Microban is an antimicrobial agent that is used to treat the HEPA filter. Microban product protection helps inhibit growth of odor-causing bacteria, mold, and mildew on the filter surface. Microban does not affect the life of the filter.
What is an Air Purifier?Air purifiers filter dust, smoke, pollen, pet dander, mold spores, and other airborne particles as small as 0.3 microns in diameter. An air purifier functions by drawing dirty air through an inlet grill, trapping particulates, and exhausting cleaner, filtered air. Some units have a washable pre-filter that traps larger airborne particles. Air then passes through a carbon filter, which captures larger particles and helps to reduce odors. The air then passes through a HEPA filter made of tightly woven fibers. Some units have electronic ionizers that further assist in particle removal. The fan then redistributes the filtered air throughout the room.
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