A fireplace is a wood-, gas-, or coal-burning appliance that is primarily used to provide
ambiance to a room. Conventional, masonry fireplaces without energy saving
features, often take more heat from a space than they put into it.
A fireplace may look warm and cozy; but, all things considered, it tends
to be relatively inefficient for home heating. Believe it or not, fireplace
efficiencies typically range from plus 10% to minus 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 should
be to install one so that you can close off the chimney when the fireplace
isn't being used. 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 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 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 tube 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
(10°C). Close all doors and warm air ducts to the room where the fireplace
is located and slightly open (about half an inch), an outside window located
near the fireplace.