What is a Merv rating?

Minimum Efficiency Reporting Value, or MERV for short, is a filter rating system devised by the American Society of Heating, Refrigeration and Air conditioning Engineers (ASHRAE) to standardize and simplify filter efficiency ratings for the public. The higher the MERV rating, the higher  the efficiency of  the filter. Simply stated, a MERV 8 filter will remove smaller particles from the air than a MERV 3 filter.