The damper is a steel or cast-iron door that opens and closes the throat of the firebox into the flue. Often, a damper becomes difficult to operate or sticks in one position. One of the most pervasive causes of a stuck damper is rust, often caused when rainwater enters the chimney through a faulty or nonexistent chimney cap.
Keeping your damper working properly is important. It regulates draft and prevents the loss of heat up the chimney. To start a fire, you must have the damper in the full-open position. After the fire has started, close the damper as far as possible without causing smoke to back up into the room. Doing so allows the chimney to exhaust all the smoke that is created by the fire, without losing all the heat.
You can clean a dirty or rusty damper with a wire brush along with lots of elbow grease. Wear safety goggles, work gloves, a hat, and old clothing. Then, with the wire brush in one hand and a flashlight in the other, use the brush to remove soot and rust buildup.
If, after cleaning the damper, it still sticks, slide a short length of pipe — about 20 to 24 inches — over the damper handle (this extends the damper handle); then beat on the pipe with a sledgehammer to break the damper loose. If the damper still refuses to budge, use a rust- and corrosion-cutting oil such as WD-40 to help dissolve the rust and corrosion at the damper’s hinges.
When the damper is operational, work it back and forth while applying a high-temperature lubricant at all the joints and moving parts. When it’s clean and in good working order, spray-paint the damper with a black high-temperature paint to prevent future rusting.
Fireplaces without dampers or with faulty dampers can be retrofitted with new dampers. Unlike the style of damper located immediately above the firebox, a retrofit model is mounted at the top of the chimney and is operated by a long chain that hangs down the chimney.