Introduction This ANSI/ASHRAE Standard 52.2 “Understanding MERV” User Guide was created by the National Air Filtration Association (NAFA), an international group of air filter distributors, manufacturers and engineers. This Guide, and the application of a particle-based contaminant removal standard prescribed by ANSI/ASHRAE Standard 52.2-2017 “Method of Testing General Ventilation Air-Cleaning Devices for Removal Efficiency by