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Fireplaces
A fireplace may look warm and cozy, but, all things considered, they tend to
be relatively inefficient for home heating. Believe it or not, fireplace
efficiency ranges from plus 10 to minus 10 percent.
The negative efficiency results from the fire "sucking" heated air from inside the home to fuel combustion. This air is then vented up the chimney, which in turn pulls cold outside air into the home through the small cracks around windows and doors.
Even when there's no fire burning, fireplaces can vent heated air, especially when there is no flue damper, or if the damper does not seal tightly, or is left open.
Here are some ways to improve fireplace efficiency.
- If your fire place does not have a damper, the first improvement is installing one so you can close off the chimney when the fireplace is not being used. Also, non-flammable "open and closed" signs that hang from the damper handle make it easy to remember if a damper is open or closed.
- Installing glass doors on your fireplace will help prevent heated room air from escaping up the chimney. The fire still draws air through vents below the doors, but only enough to burn the fuel.
- While glass doors certainly improve the overall efficiency of a fireplace and still enable you to see the fire, they do have one drawback: they partially block the direct radiant heat you feel from the fire.
- Another improvement is to duct outside air into the fireplace. This is even more effective when it is combined with the installation of glass doors. Then the fireplace does not use room air for combustion at all. If you have glass doors, the vents can be sealed completely.
- If you're building a new fireplace, install ducts around it so that cool room air is drawn in, circulated around the fire box, and ducted back into the room. The ducts are completely self-contained; and the air never mixes with the chimney smoke. If you want to have the warmed air blown out at floor level so that it will heat the room even better, install a fan in the duct system.
- If you have an existing fireplace and are not able to build a duct system around it, install a small-scale duct system in the fire box. This heat exchanger consists of hollow tubes bent into a shape that fits around the fire. Cool air from the floor enters the bottom of each tube, is heated by the fire, and convected out the top of the tubes and into the room.
- With one of the many available heat-circulating fireplace and chimney adapter systems, you can increase fireplace efficiency up to about 40 percent. These so-called fireplace inserts consist of a double-walled firebox, several air ducts, and depending on the model, a blower to speed the movement of heated air.
