Nothing matches the charm of a glowing fire in the fireplace, but owners should be aware that they may actually be paying much more for heating and cooling than they would without the fireplace.

• The Problem
• Reducing the Draft
• Alternatives to Consider

Testing conducted by a major laboratory revealed that between 80 percent and 90 percent of the heat produced by wood burned in an open fireplace is lost up the chimney. This means that for every $100 you spend for firewood, you get only $10 to $20 worth of heat. The rest goes up the chimney.

An open fireplace draws much more air than needed for combustion. As the large volume of air is drawn up the chimney, warm air from other areas of your house goes up the chimney, too. This steals heat from the other rooms and pulls cold air into the home through cracks around windows and doors and other leaky places that cannot be completely sealed off.

An open or poorly sealed damper can draw air up the chimney even when the fireplace is not in use. This can occur during both heating and cooling seasons, creating a net energy loss on an annual basis.

Cost for fireplace operation should then include not only the cost of the wood, but the cost of increased heating and cooling bills as well.

Fireplaces that use outside combustion air and have tightly fitting glass doors significantly reduce the loss of inside air. These designs, which can be costly to install, draw outside combustion air directly through vents. Although this design reduces inside air loss, it doesn't stop it.

Several products are marketed for increasing the efficiency of an existing fireplace, or as an alternative to the open fireplace. Glass doors, mentioned above, cover the opening of the fireplace to slow the flow of air up the chimney. However, glass doors also reduce the radiant heat output from the fireplace. And unless the fireplace has a direct outside air source for combustion, a certain amount of inside air must be drawn or the fire will not burn.

Tubular grates, those hollow metal (sometimes C-shaped) frames that fit into the fireplace, increase fireplace efficiency slightly by increasing the amount of usable heat from the fire. The savings associated with the grates, however, are only about $1 to $2 for every $100 worth of firewood burned. Grates equipped with fans or blowers to force more heat out will increase overall performance by 3 percent to 4 percent.

A "heatilator" type fireplace has a shell within a shell construction that provides higher efficiency heating for those who enjoy using a fireplace. The "heatilator" warms room air by circulating it around the firebox. The heated air returns to the room from the top of the shell, either with or without the help of a built-in blower. A minimum amount of inside air is needed for combustion and some models include vents for outside combustion air. These devices, which are quite expensive, fared only somewhat better in testing; the best one rated about 30 percent net efficiency.

Where wood is used as a primary source for home heating, wood stoves offer a more efficient way to burn that fuel. Although some wood stoves may prohibit the view of dancing flames, they are about twice as effective as the most efficient fireplace.