View our selection of 4-inch and 5-inch thick furnace and air conditioner filters.  These types of filters are usually referred to as media air filters. In most cases, they are housed in an “add-on” cabinet located either at the equipment, or may be installed into the duct system.  Media air filters offer much higher efficiency, and require less frequent changing than standard filters. These filters are ideal for households with pets, or occupants who have needs for better control of dust, pollen, and other respiratory irritants.