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What is HEPA Air Purifier Technology?
HEPA air purifier filters (HEPA - high efficiency particulate air filters) were originally designed in the 1940's and continue to be heavily utilized today. In order for an air filter to earn the trademarked HEPA name it must pass rigid requirements including removal of 99.97% of airborne particles 0.3 microns in diameter (1 micron = 1/25,000 inch).
The American Lung Association says that "particles of 0.3 microns diameter represent the respirable size most likely to reach and be deposited in the alveoli of the lungs; they are also the most difficult to remove by mechanical filtration." How does a HEPA air purifier work? A fan blows (or draws) air through a high tech filter, trapping particles as they pass through. A common sense but important point to remember is that air must pass through the HEPA air purifier filter in order to be cleaned. Air bypassing the filter will not be cleaned. This technology is categorized as Passive.
Particles exist in many different types and sizes. The HEPA filter is designed to trap these particles as they pass into and through the filter medium. The HEPA filter is designed to maximize air flow and still maximize particle retention. Although the filter will become less efficient over time, it is designed to effectively do its job as it slowly becomes "plugged up". Life expectancy depends on several factors, but generally is from 6 months to 5 years depending on the brand of air purifier. The size, material, and construction of the HEPA filter will ultimately determine it's longevity. Higher quality HEPA filters last longer, may be larger and thus generally cost more.
What will a HEPA filter remove? Airborne particles like Pet Allergens (.3 to 100 microns), Dust and Dust Mite Allergens (10-40 microns), Pollens (10-100 microns), Plant Spores (10-70 microns), Airborne Fungi Spores (0.5 to 5 microns), Airborne Mold Spores (2-20 microns), and larger particles of tobacco smoke (0.003 to 0.04 microns).
What won't a HEPA filter remove? Pure HEPA Filters do not remove most odors, chemicals, or gases as these particles are too small to be trapped by HEPA filters. They also are less effective against particles smaller then .01 micrometers such as tobacco smoke (0.003 to 0.04 microns). The HEPA filter will not remove most VOCs (Volatile Organic Compounds) such as paints, varnishes, cleaning supplies, glues, and adhesives, nor Microorganisms such as Viruses, Antigens, Pathogens, and Bacteria. Note: some of these substances may become trapped in the HEPA filter, but removal is not guaranteed. In the case of Microorganisms, the particle(s) may become trapped but will not necessarily be killed.
HEPA filters do work effectively for what they are intended to do. One point worth repeating: The air must pass through the HEPA air purifier filter in order to be cleaned. This generally limits the effectiveness of the purifier to the room the unit is located in. Quality air purifiers often use HEPA filters in tandem with Pre-filters, Activated Carbon Filters, and Antibacterial/Germicidal Filters and sometimes, but less often with UV Ultraviolet lights, Electrostatic Precipitators and Charged Media Filters.
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Always check the recommended life expectancy of the HEPA filter for the purifier you are considering. You will generally get what you pay for. Some HEPA filters need to be replaced often,
others last longer. The bottom line is there will be an ongoing maintenance cost with replacing them. Some warranties actually depend on changing filters regularly. Most importantly though, a HEPA purifier only works well with a properly maintained filter. All reviews in STEP3 include HEPA filter costs when applicable.
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