Honeywell FC100A1011 20 x 20 x 4.5 inch replacement media air furnace filter - MERV 11 Fiber Imported Filter Size: 20" x 20" x 5" Minimum Efficiency Reporting Value (Media Filters Only): MERV 11 Efficiency Standard: 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. Expected Duration: 6 to 12 months Fits Honeywell models: F25, F35, F100, F150