Water heater flue damper for a A.O.Smith and Whirlpool natural gas water heaters. New, never used, mounts on top of water heater to damp the warm air from going up the chimney. Keeps warm air in tank for improved efficiency. Automatically opens when burner comes on. Model number GFD-3-AOS-24, p/n 100072628. This damper came on many models including water heaters 333595, 333594. 40 and 50 gallon models. email for photos