The damper in a woodburning stove or fireplace is a control used to regulate a fire's intensity, restricting the heat escaping from the woodburner through a chimney or stovepipe by narrowing the exit. You can damper down your woodburner as an effective method to control the temperature of your fire or coals, but you should do so only under certain conditions.
Damper Down Times
You'll often need to damper down your woodburner soon after starting a fire. When starting the fire, keep the damper open fully to allow smoke to escape up the chimney. Once it's reached your desired temperature, though, you should damper down to about 1/2 to 1/4 open to keep the heat from escaping. During colder days, damper down the woodburner even further to retain as much heat as possible.
Damper down your woodburner if you plan to keep your coals burning overnight. By using your damper you limit the heat flow, which slows the burn time of your coals, keeping them from burning out completely. This should keep your coals hot enough to be able to add more wood in the morning and rekindle the fire.
You should damper down your woodburner completely when it's not being used as a fireplace, in order to prevent loss of household heat through the chimney. An open damper is like an open window as far as heat escaping from your home.
Keep in mind that the damper does not completely close the path out of the chimney. A damper is constructed with holes in it to prevent smoke and gas from leaking into the room, and does not make an adequate seal.
There are several variables that affect your damper and can cause the same damper setting to have different effects on different days. Your damper can be affected by the weather, with temperature changes and wind conditions causing a change in the draft created from the chimney or stovepipe, thus affecting the fire in the woodburner. The chimney or stovepipe itself may have an effect as well, depending on the presence of any obstructions. Even the wood you use can have an especially large effect, with moisture or age of the cut wood causing a change in the temperature of your fire or the amount of smoke generated by burning.
Experiment with your damper settings under various conditions. Experimentation is the key to knowing just how effectively your damper works and when to dampen down. Your home should contain as few people as possible when you experiment, as it may set off your fire alarms due to smoke backing up into your home.