Air filters are essential for keeping the air in your home clean and free of pollutants. All air filters require regular cleaning and filter replacement to work properly, and it is important to follow the manufacturer's recommendations for maintenance and replacement. The Minimum Efficiency Report Value (MERV) indicates the ability of a filter to capture particles larger than 0.3 to 10 microns (µm). The main difference between a HEPA filter and a True HEPA filter is their filtration efficiency.
Generally, a HEPA-type filter has an efficiency rate of 99% to capture particles as small as 2 microns, while True HEPA filters have an even better efficiency rate of 99.97% on particles as small as 0.3 microns. The HEPA-type filter is often combined with compact and inexpensive air purifiers, while the True HEPA filter is labeled with the largest and most premium air purifiers. To meet the HEPA specification, an air filter must trap 99.97 percent of all particles with a diameter of 0.3 microns or more from the air that passes through it. A filter with a MERV rating of 13 to 16 is considered a high-range MERV filter and can remove up to 75 percent of all airborne particles of 0.3 microns or more from the air.
This high particle capture rate comes at a cost: HEPA filters have more resistance to air flow than MERV filters. UltraHEPA is a commercial term used by AirDoctor that states its air purifier is “100 times more effective than HEPA air filters, capable of removing particles up to 0.003 microns in size”. HepaSilent is a patented trademark filter used by BlueAir that combines an electrostatic charge with a mechanical filter. When air is drawn into the HEPA filter, the fibers of the high-density filter trap contaminants that pass through it by direct impact, diffusion, sieving and interception.
Critics have expressed concern about the effectiveness and repair status of air filtration systems, thinking that much of the air in an aircraft cabin is recirculated. Finally, vacuum filters marketed as a HEPA type usually use a filter with a construction similar to HEPA, but without filtering efficiency. For example, a poorly designed filter with holes around the filter frame would have a very high CADR number, but would provide almost no benefit as a real filter.