Fireplaces—cozy But Costly
The home fireplace helped our ancestors make it through brutal winters. And for most of us, a crackling fire on a hearth still holds allure, especially around the holidays.
But it’s a lousy technology. It may remove more heat from a house than it produces.
A typical open, vertical-back fireplace is at best 10 percent efficient in converting wood to energy and delivering it to a room. The usual placement, on an external wall, makes matters worse, since fireplace masonry conducts heat outdoors.
A fire needs oxygen to keep going, so most of the warm air it produces gets sucked back into the fireplace and up the chimney. The resulting airflow pulls cold outside air into the house.
Typical net result: firelight dancing in the eyes of rosy-cheeked children and a higher heating bill.
SMART SHOPPER
Dampers and doors can reduce heat loss
You can reduce heat loss just by tending to a basic chimney mechanism, the damper.
Mounted in a cast-iron frame, the damper regulates air going up the chimney. Check the damper annually to make sure it fits snugly. Keep it closed when there’s no fire burning.
If you rarely use your fireplace, you can seal the flue with an inflatable stopper. Alternatively, you can stuff a rubber seat or a pillow into a plastic bag and shove that into the flue. In either case, leave an attachment—such as a red ribbon—hanging down into the fireplace to remind you the flue-stopper is there.
To cut down on the loss of heated air, you can install a vent that supplies the fireplace with air from outside the house. Glass doors and fireplace covers also reduce heat loss. Covers are cheaper, but you can only use them when there’s no fire.
Good doors should have a rigid frame and a seal that fits snugly against the fireplace rim. Closing the doors during a burn reduces radiant heat reaching the room, but it also cuts the amount of warm air whooshing up the chimney.
DOLLARS & SENSE
Inserts are efficient, but be wary of unvented models
Among all the means of improving fireplace efficiency, inserts make the biggest difference.
Inserts may burn wood, pellets, or natural gas. Some models have catalytic converters that boost combustion efficiency. Some have fans to blow air around the unit and out into the room. The most efficient, safest inserts have double walls with space between them where heated air circulates, plus a connection with the flue to ensure smoke dispersal.
Gas-burning fireplace inserts have grown in popularity, but beware of unvented models. They deplete room oxygen, and may produce carbon monoxide and excessive water vapor. A vented gas-fired insert with a sealed combustion unit is safer.
