Size 6x6" Ceiling Radiation Damper Rectangular. Damper is for vertical penetration through ceiling run ductwork and closes by gravity. Spring Loaded assisted the damper is made smaller than the listed duct size and is mounted inside the duct in air stream. Union Made, UL Listed, Insulated Blades. Those dampers over 80 sq. inches have ceramic insulation on backs of blades . 1 On Hand