Heating and cooling costs climb every year, which makes it worth closing off the places where conditioned air escapes your home. An open chimney flue is one of the biggest. A chimney damper seals that flue when the fireplace isn't in use, keeping warm air in during winter and cool air in during summer.
How a Damper Works
Dampers come in two main designs. A throat damper sits just above the firebox, while a top-sealing damper — often called a chimney damper cap — mounts at the very top of the chimney. Both are operated by a chain or a turning knob. Whichever type you have, use it consistently: leaving the damper open when there's no fire is the same as leaving a window open year-round.
More Than Energy Savings
Energy conservation is the main reason to install a damper, but it isn't the only one. A closed damper also blocks animals, birds and debris from entering your home through the flue. An uncapped chimney is an attractive nesting site — warm, sheltered and safe from predators — and a damper above the firebox forms a barrier between whatever gets in and your living room. Be aware that larger animals such as raccoons can sometimes force a damper open, which is why a chimney cap is worth pairing with one.
Dampers also keep rainwater and falling debris out of the firebox. The smoke shelf behind the top of the firebox catches most of it, but once that shelf fills up, the overflow lands in your fireplace. A damper stops it before it gets that far.
Summer and Winter Use
In warm months, a closed damper keeps air-conditioned air from drifting up the flue. Paired with tight-sealing glass fireplace doors, it makes a noticeable difference to cooling costs. In winter, if you're heating with a furnace and the fireplace is idle, the same seal stops your heated air from being drawn out through an unused chimney.
Top-Sealing Damper Caps
A top-sealing damper installs at the top of the chimney and is operated by a chain running down to the firebox. The Energy Top Chimney Damper is one common design — open, it resembles a chimney cap; closed, the lid drops onto the flue opening and all but disappears from view. The Seal Tight Chimney Damper works similarly, using a single turning plate to open and close the flue without the appearance of a cap on the chimney.
One Drawback Worth Knowing
Top-sealing dampers can't be closed immediately after a fire. Wood keeps smoldering for hours after the flames die down, so the damper has to stay open until it's fully out. If rain or snow falls during that window, moisture gets into the chimney. And because most damper caps have no wire mesh, a damper left open in spring offers no protection against animals or debris.
The fix is to install a chimney cap over the damper. It has to be large enough to clear the damper's opening and closing action, which makes it a bigger cap than usual — but even for throat dampers mounted above the firebox, a cap is worth having for exactly this reason.