What Is a MERV Rating?

The EPA says Minimum Efficiency Reporting Values, or MERVs, report an air filter's ability to capture particles between 0.3 and 10 microns, which helps in comparing filters for furnaces and central heating, ventilation and air conditioning systems. The rating comes from a test method developed by the American Society of Heating, Refrigerating, and Air Conditioning Engineers, and the higher the MERV rating, the better the filter is at trapping specific sizes of particles.

The EPA says many home HVAC systems have a MERV 8 filter installed as the default. If you upgrade, it advises choosing a filter with at least a MERV 13 rating, or as high a rating as your system fan and filter slot can accommodate, and notes that filters rated MERV 13 and above are required to demonstrate at least 50 percent removal efficiency for the smallest particles tested.

Check the system first. The EPA says most furnaces and HVAC systems can accommodate a MERV 13 filter without creating equipment problems if the filter is replaced frequently, but that HVAC systems are not commonly labeled with filter recommendations, so a professional HVAC technician may be needed to determine the most efficient filter your system can use. It advises replacing filters according to the manufacturer's recommendations, which typically call for replacement every 60 to 90 days, changing them more often if they look heavily soiled, and remembering that HVAC systems filter the air only when the fan is running.