Fireplaces

Flickering flames, glowing embers, the essence of wood smoke: nothing is quite as cozy as a fire on a cold winter day. Of course for a fire, a house needs a fireplace that will safely contain it, encourage the fuel to burn, exhaust smoke and deliver warmth to the room. To handle the varied tasks, a fireplace has several essential components, as shown in the illustration.

A traditional fireplace heats by radiation. Radiant heat from the fire warms objects in a room, not the air. Heat is retained by the walls of the fireplace, too, and released slowly into the room. Unfortunately, most traditional fireplaces are notoriously inefficient at heating. They may actually increase drafts in a house by drawing room air through the mouth of the fireplace and sending it, along with as much as 90% of the heat generated by the fire, up the chimney.

To cut heat loss and drafts, some contemporary fireplaces have glass doors; in addition, they draw combustion air directly from outdoors so the fire doesn't try to steal it from the room. Some efficient models also have vents that pipe room air past the firebox so it can be heated, then return it to the room. And some fireplaces are specially designed to maximize radiant heat delivery and retention.

A zero-clearance fireplace, prefabricated from metal, is installed in a standard, wood-frame wall. Fresh combustion air is brought in from outdoors through a duct. Room air is warmed as it circulates through a heat exchanger and is blown back into the room. A metal double- or triple-wall chimney flue typically carries smoke and combustion gasses up through the house and out the roof.

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