What is an efficiency or MERV rating?

Most filters are labeled with a MERV (Minimum Efficiency Reporting Value) rating number, which measures a filter's ability to trap particles ranging in size from 3.0 microns to 10.0 microns. This number is derived from a test method designed by the American Society of Heating, Refrigerating, and Air Conditioning Engineers (ASHRAE) and is intended to help people compare filters.

Residential filters commonly have MERV ratings of 1-16. The higher...

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