WHAT IS MERV? The term “MERV” (Minimum Efficiency Reporting Value) was created and is used by “ASHRAE” (American Society of Heating Refrigerating and Air Conditioning Engineers). The “MERV 13” gets its rating from undergoing strict tests and passing certain requirements. The MERV 13 requires filters of that name to trap particles ranging in size from up to 10 microns in diameter down to 0.3 microns in diameter (smaller than the thinnest human hair). In other words, this is a highly efficient filter capable of trapping 90% of airborne particles and allergens such as mold spores, dust particulates, pollen spores, pet dander, and bacteria down to 0.3 microns in size.