All wood-burning fireplaces have a damper, and their primary purpose is to close off the chimney. The damper should be open all the way whenever you have a fire -- or your house will be filled with smoke from an inefficiently burning fire -- and it should be closed when there's no fire, to prevent heat loss. However, if you have a gas insert or log kit in a traditional fireplace, the damper should remain open at all times to prevent a deadly hazard.
Types of Dampers
Your chimney may have one or both of the two available types of dampers:
The throat-mount damper is located at the top of the fireplace, where the walls taper to form the chimney. The point at which the damper is located -- the throat -- must be the proper size for the most efficient operation of the fireplace, and installing a damper is often a way to compensate for a less-than-optimal throat. These dampers can be operated by a ratcheting push or lift rod, or a screw-type rotary control.
Top-mount dampers fit on top of the chimney flue. Homeowners often elect to replace old throat-mount dampers with top-mount models, which typically create a better air seal and also keep moisture and animals from getting into the chimney when there's no fire. Top-mount dampers are spring-loaded, and the default position is open. You have to pull chain and secure the chain on a hook on the side of the firebox to close it.
Checking the Damper
If you suspect your throat- or top-mount damper isn't working properly, a number of simple tests can help:
- Take a look. Poke your head inside the fireplace and look up through the chimney. Use a flashlight if necessary. If a throat-mount damper is closed, you should see it as a barrier just above your head. If it's open, you'll be able to see into the flue. To visually check a top-mount damper, you may be able to see its position while you're standing on the ground. Binoculars can help here. Otherwise, you have to go on the roof for a good look, but this usually isn't necessary unless there's a problem with the damper.
- Check the controls. Push in the push rod or lift the lift rod all the way. If the damper has a rotary control, turn it clockwise as far as it goes. If the damper is a top-mount one, pull on the chain; if there's play in it and it can be pulled down before springing back up, the damper is open.
- Feel the breeze. Put your hand in the firebox. You should easily be able to feel air circulating up through the chimney. In some cases -- if the fireplace is in the basement, for example, you may even feel air coming down. If either the throat- or top-mount damper is closed, you shouldn't feel any air.
- Light a fire. You'll know that the damper is closed if you're able to get a fire going, because smoke will billow out from the chimney and fill the room. Open the damper, and it will go out through the chimney.
Many homeowners choose to convert their regular fireplace to one that burns gas logs, and when you make this conversion, you must leave the damper permanently open to prevent leaking gases from circulating in the house. Keeping the damper open wastes heat, though. You can avoid the need to do this by installing clips on the damper that prevent it from closing all the way, but according to one home inspector, the clips are a poor substitute for keeping the damper open.