In a masonry fireplace, the damper controls heat, and gas flow and forms a barrier to back draft in the firebox. When open, it allows gases and smoke to pass through from the fire chamber to the smoke chamber. When closed, a damper reduces heat loss and directs heat into the room, eliminates downdrafts, and keeps animals, wind, and rain out of the fireplace, home, and in some cases, the chimney. Five types of dampers can be installed in a masonry fireplace: blade, form, high dome (high form), universal (square form), and chimney-top. DAMPER OPTIONS The cast-iron blade damper has a valve plate with a welded handle that extends into the firebox for opening and closing. The form damper generally is made of steel. It incorporates a blade damper inside a metal box form that serves as a throat between the firebox and flue, saving the labor and costs of building a complete smoke chamber. High-dome and universal dampers are good choices for multi-opening fireplaces because they cover more of the firebox and throat area. CHIMNEY-TOP DAMPERS Chimney-top dampers fall into a separate class from conventional dampers. Like high-dome and universal dampers, they can be used with any type of fireplace, but protect it from the top rather than from inside the flue. Because of this, they also function as chimney caps when closed. PROPER INSTALLATION When a damper is installed correctly, it should last the life of the house. Incorrect installation of a damper can create potential smoke problems, crack internal masonry and masonry facing, and cause the damper to burn out.