MERV RATINGS EXPLAINED Recently the American Society of Heating Refrigeration and Air Conditioning Engineers (ASHRAE) and the air filter industry have come up with a standardized rating system, based on the European concept, of a MERV rating for each type of air filter. This numbering system makes it easier to evaluate and compare mechanical air filters and will hopefully eliminate some of the confusion regarding the overall effectiveness of any type of a mechanical air filter on removing airborne particulates, especially those that are less than 2 microns in size. Minimum Efficiency Reporting Values (MERV) Group Number MERV Rating E1 Average Particle Size Efficiency (PSE) 0.3-1.0 Microns E2 Average particle Size Efficiency (PSE) 1.0-3.0 Microns E3 Average Particle Size Efficiency (PSE) 3.0-10.0 Microns Average Arrestance (ASHRAE 52.1) Minimum Final Resistance (in. W.G.) 1 MERV 1 MERV 2 MERV 3 MERV 4 - - - - - - - - Less than 20% Less than 20% Less than 20% Less than 20% Less than 65% 65-36.9% 70-74.9% 75% or greater 0.3m 0.3m 0.3m 0.3m 2 MERV 5 MERV 6 MERV 7 MERV 8 - - - - - - - - 20%-34.9% 35%-49.9% 50%-69.9% 70%-84.9% - - - - 0.6m 0.6m 0.6m 0.6m 3 MERV 9 MERV 10 MERV 11 MERV 12 - - - - Less than 50% 50%-64.9% 65%-79.9% 80%-89.9% 85% or greater 85% or greater 85% or greater 85% or greater - - - - 1.0m 1.0m 1.0m 1.0m 4 MERV 13 MERV 14 MERV 15 MERV 16 Less than 75% 75%-84.9% 85%-94.9% 95% or greater 90% or greater 90% or greater 90% or greater 90% or greater 90% or greater 90% or greater 90% or greater 90% or greater - - - - 1.4m 1.4m 1.4m 1.4m source: www.pureairsystems.com           source: Lennox Industries