Merv Ratings

Written by Norene Anderson
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MERV ratings are determined by ASHRAE Standard 52.2. This Standard is set to determine the efficiency of a filter in capturing different sized particles. The Standard was devised out of a need for a common comparison of various air filters. Various filtering manufacturers may claim a product will remove certain pollutants and then not produce when you get the product home. This standard states that ASHRAE has examined the product and determined the size of particles it will retain.

The MERV ratings make it a lot easier to compare prices on like items. If a unit retains less than 20 percent of particles in the 3 to 10 micrometer range, the rating of MERV 1 is determined by ASHRAE. If a unit retains greater than 90 percent of the same size, a MERV 12 rating is given. A MERV 11 rating is assigned to filters retaining 50 to 65 percent of particles in the range of 1 to 3 micrometers.

MERV Ratings by ASHRAE

MERV ratings for home use stop at 12. Anything over 12 is for commercial buildings and places such as hospitals. This is a good indicator to determine if the product you are considering is truly for home use. The closer you can get to a 12, the better for overall improvement in the air quality.

There are particular filter types for the different levels of MERV scores. For example, a MERV 1 to 4 rating may be fiberglass or synthetic. A MERV 9 to 12 rating is typically a rigid or cartridge style. Replacement filters are available in all ratings to make breathing easier in any home environment.


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