Periodically check the structural integrity of your fireplace and also of the chimney. Inspect the inside with a flashlight for loose bricks, gaps in the mortar, or an obstruction in the chimney. Repair any defects.
Try to operate the damper. This movable plate for adjusting the draft is kept open when a fire is burning; when there is no fire, it is closed to minimize loss of room heat. It should work easily and shut snugly. If it is stiff, spray its hinge or pivot points with silicone lubricant and manipulate the handle until it works freely. If the damper doesn’t close completely, remove creosote deposits around it with a putty knife. If there are still gaps when it is shut, fill the spaces with furnace cement.
If smoke enters the room
The position and size of the damper are important. It should be 6 to 8 inches above the lintel and the same length as the
width of the fireplace opening; otherwise smoke will flow into the room. If the position is wrong, adding a metal shield or hood at the top of the fireplace opening may solve the problem. If the damper is not long enough, have a mason either install a correct one or make the fireplace opening smaller.
A too-shallow fireplace may cause smoking. Try raising the and irons or the grate on bricks, or use a grate that holds the logs nearer the back wall. If none of the above solves the problem, consult an expert for other solutions.