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The Fireplace’s Dirty Little Secret

I have been using my open masonry fireplace to help lower my heating, but it is not helping. The house actually feels colder. Is there anything I can do?—Thomas M.

People seldom realize that most open fireplaces draw more heat out of a house than they produce to warm it. This makes the furnace or heat pump run longer, increasing utility bills.

Even though you feel toasty directly in front of the flames, the rest of the rooms get chilly. All the room air drawn up the chimney is replaced by cold outdoor air leaking in through cracks and gaps in your home.

There are several simple ways to make your fireplace more efficient and change it into an energy producer and money saver. If you have made general improvements to your home to make it more efficient and airtight, this may actually make the fireplace worse and may create a backdrafting and smoky condition.

The two key areas of fireplace efficiency improvements are:

1. reducing the amount of already-heated room air lost up the chimney, and

2. directing more heat from the fire out into the room.

After you make your fireplace improvements, running your furnace blower on continuous air circulation when the fire is burning will help distribute the heated air from the fireplace throughout your home.

The most heated room air is lost up chimneys when there is no fire burning. This occurs 24 hours a day because of a nonexistent or poorly sealed chimney damper.

To seal the chimney better and provide some insulation, I use an inflatable chimney balloon (also called chimney pillow) in my fireplace. You place it in the flue, blow it up like a mini-air mattress, and it expands against the sides to seal air leaks.

Another option is a tight-sealing damper assembly mounted on the chimney top. Long stainless-steel cables hang down the chimney and attach inside the fireplace opening to open and close it. It is sealed to the top of the chimney with silicone caulk, so it also functions as a protective chimney cap. Chimney exhaust fans also help and can reduce a smoky fireplace condition if it lacks adequate draft.

When you are burning a fire, tight-fitting glass fireplace doors with adjustable air openings are imperative. Some doors use magnets and others use cams to hold them in the tightly closed position. High-temperature silicon gaskets provide an excellent long-lasting seal.

Installing a heat-circulating grate in the fireplace will make the greatest improvement in usable heat output. The grate is made of steel pipes with a built-in fan that draws cool room air in one side and blows heated air out the other.

Models with a built-in thermostat and variable-speed blower provide the most control over the heat output and the sound level. Set the blower to high speed when the fire is really raging. The thermostat turns the blower on automatically at 110 degrees and off at 90 degrees, so it won’t continue to run as the fire burns down and cools off.

If you have access from a crawlspace or basement beneath the fireplace, run a duct from outdoors to the front of the fireplace. Install a tight-sealing adjustable register cover over it. When burning a fire, open the register so outdoor air will be drawn in for combustion. This reduces the amount of heated room air being drawn from your home.

If you don’t use your fireplace often and you like an open hearth, set the furnace thermostat back and crack open a window in that room for combustion air. Placing a heavy cast-iron plate (fireback) in the back of the fireplace helps radiate more of the fire’s heat into the room. Most firebacks have decorative patterns cast into the face.

Mail requests and questions to James Dulley, Kentucky Living, 6906 Royalgreen Drive, Cincinnati, OH 45244, or visit www.dulley.com.

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