Chim-A-Lator 052020 20" x 20" Deluxe Fireplace Damper with 3/4 Mesh easily mounts on top of a masonry fireplace flue and is operated by a convenient, adjustable regulator installed on the side wall of the fireplace. It is far more efficient than conventional cast iron dampers and the ideal replacement for old defective fireplace dampers. Proven for over 40 years to be the most trouble free top dealing damper.