Abstract: A fire damper assembly, used in a heating, ventilating and air conditioning system, includes a sheet metal outer frame circumferentially surrounding a commercially available, rectangular fire damper. Angle iron retainers mounted interior of the outer frame and front and back of the fire damper retain the fire damper along the depth of the outer frame. The outer frame is intended to be sealed directly or in a sealed duct in a fire resistant wall opening or penetration provided for passage of air of the heating, ventilating and air conditioning system. The outer frame has a height and width sufficient to accommodate the height and width of the fire damper plus the required thermal expansion of the fire damper to insure its proper operation under the heat or increased temperature of a fire. The angle irons close the thermal expansion spaces to passage of air and fire.