Honeywell FC100A1003 16" X 20" Media Air Filter, MERV 11 New MERV 10 (at 492 FPM) performance with lower pressure drop at no additional cost! Efficiency ratings are based on American Society of Heating, Refrigerating and Air-Conditioning Engineers Standard 52.2 1999! Efficiency ranges are defined for small particles, E1=0.3 to 1.0 microns; medium particles, E2=1.0 to 3.0 microns; and large particles, E3=3.0 to 10.0 microns