4 Inch Air Filters

4 inch furnace filters are available in many standard and non standard sizes such as 16 x 25 x 4 furnace filter, 20 x 20x 4 furnace filter, 20 x 25 x 4 furnace filter and 24 x 24 x 4 furnace filters. The length and width of furnace filters are reversible (i.e. A 16x20x4 is the same as a 20x16x4).