Spotlight on Filtration: Understanding MERV Rating

Facility maintenance decisions

The Minimum Efficiency Report Value (MERV) is a critical metric for selecting the right filter for your facility. Here’s what you need to know.

The efficiency of the air filter is assessed based on the Minimum Efficiency Report Value (MERV). Values ​​range from one to 20. The higher the MERV rating, the better the filtration.

For example, a filter with a MERV rating between five and eight removes 80 to 95 percent of particles in the airstream that are 3 microns or larger. A filter with a MERV rating between nine and 12 removes 90 percent or more of particles 1 micron or larger. A filter with an MERV value of more than 13 can remove 95 percent or more of particles 0.3 microns or larger. Higher MERV ratings can be achieved through the use of High Efficiency Particulate Air (HEPA) filters

While a higher MERV rating means higher filtration efficiency, it also means greater resistance to the airflow in the system. This resistance must be offset by increased fan power consumption, so managers must weigh the need to remove particles of a certain size against the ability of the HVAC system to deliver the necessary airflow to the occupied space.

ASHRAE and the CDC recommend a minimum MERV rating of 13 for most commercial and institutional applications.

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