Energy-Efficient Fireplaces

There's nothing quite like the warmth and ambiance of a fireplace in the winter. But although they are attractive to look at and sit near, regular fireplaces are actually very wasteful of your energy. Fireplaces are very inefficient because they draw warm, conditioned air up the chimney, pull cold outside air into the home, and cause the main heating system to work harder and longer.

How They Work

A fire requires a constant flow of oxygen (or "combustion air") to remain lit. Because heated air rises up the chimney, a natural suction is formed and warmed air is actually pulled right up the chimney and outside instead of being distributed into the room. This process is called the "chimney" or "stack" effect. Approximately 80% of the air heated by the fireplace is lost up the chimney because the fireplace is pulling the heated air back in for combustion.

Air can also be pulled into the house from outside under doors, around windows, or through other openings, as a result of the chimney effect. This can increase the demands on (and cost of operating) your heating system since it must operate longer to condition the cold, outside air.

Energy-Efficient Improvements

There are several ways to improve the energy efficiency of your fireplace, and your comfort as well.

• Chimney Dampers - The proper use and operation of the chimney damper can dramatically reduce the chimney effect. The damper should be tightly closed when the fireplace is not in use. The damper should be checked periodically to assure proper closure. If the fireplace is never used, the damper should be sealed with weatherstripping and the chimney stuffed with fiberglass insulation. Please Note: This material must be removed from the chimney before a fire is lit in the fireplace.
• Glass Doors - Glass doors act as a barrier against warmed air returning up the chimney. Some models of glass doors are equipped with small vents along the bottom or sides to allow a controlled amount of combustion airflow into the fireplace. The glass allows the heat from the fire to radiate into the room. Because glass doors reduce the amount of conditioned air that is drawn up the chimney, they also reduce infiltration of outside air into the home.
• Outside Combustion Air - Since fireplaces draw so much air up the chimney, the use of an outside combustion air vent will greatly improve fireplace efficiency. When an outside combustion air vent is installed, the air needed to keep the fire lit is brought in from outside, not from inside the heated room. This greatly reduces the amount of conditioned air being drawn up the chimney and the resulting infiltration of outside air. The best alternative for an efficient fireplace is to use an outside combustion air vent in conjunction with glass doors. All the heat being radiated from the fire stays inside the room, and none is drawn back into the fireplace.
• Fireplace Inserts - Fireplace inserts or wood stoves are available to fit into an existing fireplace. These inserts are equipped with glass or metal doors, outside combustion air vents, and heat circulation blowers. Fireplace inserts dramatically improve fireplace efficiency by blowing heat from the fire into the room and by limiting the amount of heat and conditioned air lost up the chimney. Fireplace inserts are recommended for fireplaces that are regularly used. Before installing a fireplace insert, be sure to check the manufacturer's safety specifications and make sure the fireplace insert is compatible with the existing chimney or vent flue.