Dealing with the Damper
The damper is a steel or cast-iron door that opens or closes the throat of the firebox into the flue. It regulates draft and prevents the loss of heat up the chimney.
The fireplace damper must be in the full open position in order to start a fire. Once the fire has started, the damper should be closed down 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, but not the heat.
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 non-existent chimney cap.
A dirty or rusty damper can best be cleaned using a wire brush along with lots of elbow grease. But, be advised that you're not going to like it. Wearing safety goggles, work gloves, a hat and old clothing; armed with a wire brush in one hand and a flashlight in the other, use the wire brush to remove soot and rust buildup.
If after cleaning the damper, it still sticks, it's time for a little horsepower in the form of a pipe and small sledgehammer. Slide a short length of pipe -- about 20 to 24 inches -- over the damper handle. This extends the damper handle and allows you to beat on the pipe with the sledgehammer to break the damper loose. If the damper still refuses to budge, use cutting oil to help dissolve the rust.
Once the damper is operational, work it back and forth while applying a high-temperature lubricant at all of the joints and moving parts. Once clean and in good operating 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 a new damper. 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.