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.