Q15. What does MERV mean?

Minimum Reporting Efficiency Value (for air filters). It is a standardized single rating value of an air filter, measured at a linear airflow speed of 500 fpm (approximately 8 m/s)  that gives a relative metric of how well an air filter performs at removing differently sized particles from the air.  Ratings typically range from MERV-6 (dust absorption) to MERV-20 (virus absorption).  The actual MERV number of a filter describes a percent-of-absorption curve over a range of particle sizes [view here in Part 3].