Fireplace is an Inefficient Way to Warm Up Your Home

Dear Action Line: You haven't had anything on fireplace safety. If there are power outages from this ice storm, lots of people will be using their fireplaces for the first time. -- L.T., Tulsa.

Fireplaces waste energy: The U.S. Department of Energy's Office of Energy Efficiency and Renewable Energy -- www.eere.energy.gov -- says the best way to save energy with a fireplace is to seal it up. Fireplaces might have provided enough heat for drafty 18th century cabins but are grossly inefficient at heating modern, airtight homes. We have them mostly for ambiance but they are the poorest choice in heating technology, removing more heat from the house than they produce. They superheat the room they're in while the rest of the house becomes as cold as the outdoors. This is because the strong exhaust-suction they create pulls cold air in through gaps around windows, doors and attic fan openings.

Low efficiency: A fireplace with an open front is just 10 to 20 percent efficient at turning wood into heat, meaning 90 percent of produced heat goes up the chimney. The typical fireplace, its mouth covered by glass doors, mostly provides radiant heat -- that produced in surrounding objects by infrared light waves from the fire. To provide the fire a secondary source of combustion air, open the outside ash-dump door (usually at ground level on the outside of the chimney). Remember to close it when the fire is out, to keep mice out.

Damper: A fireplace has a damper -- a door-like vent in the throat of the chimney just above the smoke shelf and fire chamber. It is enclosed in a cast iron frame with a hinged lid that opens and closes to vary the chimney's throat opening and the speed of exhaust gases up the flue. The damper regulates the amount of air going up the chimney, controlling the amount of air the fire receives. When the fireplace is not in use, keep the damper shut to keep room air from going in.

Flue sealers: If you never use your fireplace, put an airtight cover over its mouth or, better still, install a flue sealer to prevent heat loss up the chimney. Buy an inflatable stopper to insert at the smoke shelf. Put a sign on the fire grate reminding yourself the flue is sealed.

Glass doors: Fireplace glass-doors and insulated covers are economical alternatives to losing heat up the chimney but unless the door glass is kept sparkling-clean, they also rob heat from the fire. J.W. Shelton, in "Measured Performance of Fireplaces and Fireplace Accessories" (1978), observed, "Glass doors are the most misunderstood fireplace accessory. The usual rationale for glass doors is they will allow a view of the fire while reducing the flow of room air up the chimney. What is often not realized is with the type of glass normally used, the doors block much of the infrared radiation. With the competing effects of reduced heat radiation (bad) and reduced room air loss (good) the only way to know the net effect is to measure it."

Open ash-dump door: He measured and found with glass doors closed and a fire using 10 to 15 pounds of wood per hour, there was a 40-50 percent reduction in total gross heat output compared to the same size fire in the same fireplace with the glass doors open. The gross energy efficiency with glass doors closed was about 10 percent, compared to about 20 percent with the doors open. So the best thing to do with a fireplace is run it with doors open and ash- dump door wide open for combustion air -- reducing the exhaust suction on the home's perimeter. Draw the spark net closed and keep combustibles back from the opening. Never leave a fireplace fire unattended.

Submit Action Line questions to 699-8888 or by e-mail at phil.mulkins@tulsaworld.com. Action Line pursues consumer complaints submitted with photocopies of documentation to Tulsa World Action Line, P.O. Box 1770, Tulsa, OK 74102-1770.

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