A fireplace damper serves the same purpose as a window. When open, it allows air to blow out through the fireplace chimney. When closed, it keeps the warmed air inside the fireplace and house. It should be open when a fire is burning and closed once the fire is completely out. Different types of fireplace dampers are associated with different types of fireplaces. The most common are throat mount and top mount. Custom-made dampers or no damper is present at all for use in unconventionally designed fireplaces.
A throat-mount damper is called so because it is situated at the throat of the firebox and chimney. Throat-mount dampers are inflatable devices that are placed in the near vicinity of the flue and used to seal off any extraneous air that can slip in around the flue. Throat-mount dampers are aftermarket purchases that are installed easily. Get the correct size for your inner fireplace walls to ensure the best sealant. Throat-mount dampers do not keep birds and critters from nesting in the upper half of the chimney, and they can also be punctured with considerable force. They range in price from $40 to $100, as of December 2010, and do not require professional installation.
Top-mount dampers fit over the top of the chimney. They are made of metals such as iron or steel and serve as a type of gateway or cap that opens and closes when a fire is burning. A rubber-type gasket usually surrounds the outer edge of the damper to help in closing off intruding gusts of air. Resting on the very top of the chimney prevents many problems from nesting animals and debris. They range is cost from $150 to several hundred and require professional installation. While more expensive than the throat-mount dampers, they are also more efficient and durable.
Fireplaces with large flues or designed in an unconventional manner require custom-made dampers. Those of unconventional size and dimension must fit the damper perfectly. Even the slightest gap can cause frigid drafts and allow for animals to nest inside. These types of dampers are usually priced quite high, several hundred dollars to $1,500 at the lowest range.