What's in a MERV?
MERV is an industry standard rating for air filters that measures their ability to trap particles ranging in size from 3 to 10 microns. Home air filters commonly have MERV ratings from 1 to 12 — the higher the rating, the more efficient the air filter is at trapping particles.
To determine a MERV, solid particles of varying sizes are introduced into the test system, upstream from the test air filter. A laser particle counter alternately samples air upstream and downstream from the test filter. This is done on the clean filter and after five dust feedings. The lowest efficiency for each range is used to determine the Composite Minimum Efficiency and assign a MERV rating