Filtrete 16-in W x 20-in L x 4-in 12 MERV 1550 MPR Allergen, Bacteria and Virus Electrostatic Pleated Air Filter in the Air Filters department at Lowes.com
BestAir 16 x 20 x 4 Honeywell FPR 4 Air Cleaner Filter HW1620-8R - The Home Depot
4 Inch Furnace Filters | unitedfilter.com - United Filter
Honeywell Home 16 x 20 x 4 Pleated Furnace Air Filter FPR 10, MERV 12 CF200D1620 - The Home Depot