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What do MERV ratings mean?

Minimum efficiency reporting value, commonly known as MERV rating, is a measurement scale for air filters designed by the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) to rate filter effectiveness.

The scale "represents a quantum leap in the precision and accuracy of air-cleaner ratings"[1] and allows for improved health, reduced cost and energy efficiency in heating, ventilation and air conditioning (HVAC) design. 

The MERV rating is from 1 to 16. Higher MERV ratings correspond to a greater percentage of particles captured on each pass, with a MERV 16 filter capturing more than 95% of particles over the full range. A consideration in selecting a high MERV filter is air flow through the your HVAC system. Leaving a dirty air filter in place or using a filter that is too restrictive may result in low air flow that could damage your system and create comfort issues.

Table of MERV ratings and particle size

1. Wilkinson, Ron. "Air Filters: New Facilities, New Standard" (PDF). Retrieved 2007-03-29

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