Home Ownership Most of Canada's one million fireplaces are old-fashioned open hearths. Their appetite for warm air is limitless and their reputation for sucking petro-dollars up the chimney is well-known. Fireplace inserts offer a compromise — charming open fires and a partially closed-off chimney. As wood-heat alternatives go, they're much more interesting than wood stoves, but less efficient.

Fireplace inefficiency can be narrowed down to three causes. First, an open fireplace draws

unlimited combustion air from the interior of your house. It burns hot and quickly, using a lot of wood. Second, fireplace flues are large, producing tremendous updrafts that draw warm air from the house. And third, when the fire has burned down at night, the open flue continues to draw hot air outside.

Fireplaces not only lose a lot of heat up the chimney — they are also limited heaters. When you sit in front of a fire, your face is heated by radiant energy and your back stays cool. Like sunshine, radiant energy warms any surface it touches without warming the air. Heating the room evenly requires heating by conduction or convection. This will happen naturally, albeit slowly, as heated surfaces warm the air around them. Warm air rises and circulates, thereby producing heating by convection. Changing your fireplace into an energy credit often includes converting radiant heat to convected heat with some type of air circulation system.




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December 4, 2008