"This Hamilton Home Products Return Air Coil Box is a knock-down design and can easily be assembled and attached to the top of the mobile home electric furnace, Item#s 27436, 27437, 700250 and 700251. Includes a louvered front door with door and top return air filters. Material Type Steel, Mounting Type Top, Fuel Type Electric, Length in. 22 3/4, Product Style Air returns, Mounting Hardware Included Yes, Color Galvanized. Includes one 1in. x 20in. x 20in. door filter and one 2in. x 20in. x 24in. top filter For use with mobile home coils with a maximum height of 26in."