The term “chimney plug” is used in reference to several different devices which can be used in a chimney. In one sense, a chimney plug or chimney cap is a piece of equipment which can be fitted to a chimney or thimble opening to seal it when it is no longer in use, ensuring that drafts are not allowed to flow through the hole. In other sense, the term is used to refer to a device which seals a chimney when fires are not going, preventing drafts from traveling down the chimney. Both are designed to reduce energy costs by minimizing heat loss through openings in a structure which are not being used.
Chimney plugs used to stop up unused chimney openings are available at many construction and home supply stores, and they can also be ordered directly from the manufacturer. In this case, the chimney plug is designed to screw or snap into an opening to block it. The device may include ceramic or felt liners which insulate and create a tight seal. One case in which someone might use a chimney plug is when a stove which vented out a wall is removed, leaving the opening in the wall behind; the hole can be easily sealed with a chimney plug.
Chimney plugs designed to be inserted into a chimney when it is not in use are sometimes known as chimney pillows. They are made from inflatable materials which swell to fill the chimney below the damper, preventing heat from rising up the chimney and blocking cold drafts which might come down the chimney. When someone wants to light a fire, the device is removed; most also have a safety feature which causes the device to deflate when exposed to heat, in the event that it is accidentally left in place and a fire is lit.
Other chimney plugs which prevent heat loss through a chimney when a fire is not lit may be designed to be left in place, making them easier to use. These devices fit to the damper to make a tighter seal. When a fire is lit, the damper is opened to create draft to control the fire. When a fire is not lit, the damper is closed, and the chimney plug makes a snug seal to prevent heat loss.
Chimneys are a common source for heat loss in the home. Many people are aware that heat can be lost around windows and doors, and take steps such as caulking, installing weatherstripping, or putting in double paned windows to prevent heat loss of this type. However, an open chimney can allow a surprising amount of heat out, and permit cold air to move in, raising energy costs as people struggle to control the temperature.