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 10+ to -10%.
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 pulls cold outside air into the home through the small cracks around windows and doors.
Even when there is no fire burning, fireplaces can vent heated air - especially when there is no flue damper, if the damper does not seal tightly, or is left open.
Here are some ways to improve fireplace efficiency:
- If your fireplace 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 are building a new fireplace, install ducts around it, so that cool room air is drawn in, circulated around the firebox, 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 firebox. 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%. 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.
You should not use a fireplace for supplemental heating, unless you take one or more of the following measures:
- Lower the house thermostat to 50°F.
- Close all doors and warm air ducts to the room where the fireplace is located and slightly "open" (about one-half an inch), an outside window located near the fireplace.
When using any fuel-burning fireplace, be sure to check the manufacturer's operating instructions. As an added safety precaution, installation of a Carbon Monoxide Detector is recommended.
A cozy and safe alternative to a wood or gas fireplace is an electric fireplace, which requires no chimney or other venting. If you only want one for decorative purposes anyway, some of the newer electric fireplaces are amazingly realistic. You might have a fireplace store in your town where you can see one of these new fireplaces, or search the Internet to see pictures of various models or find a supplier.