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Use Heat efficiently
The heat created by a fire can be used in several ways. One is to provide a masonry mass that absorbs, stores, and slowly re-radiates heat energy back
into the room. This method provides a slow, low intensity heat source long after the fire is out. By the positioning fireplace wholly within the building envelope the thermal mass effect can be made more effective
than if it was placed on the outside wall where heat would be lost. Another method is to provide high intensity radiant heat while the fire is burning. Rumford and Rosin type fireplaces are designed to maximize the
amount of radiant heat emitted by the fireplace. They have tall, wide openings, very shallow fireboxes, and widely splayed coves or jambs to reflect as much high intensity radiant heat as possible. For more
information on these types of fireplaces consult BIA Technical note #19C or visit http://www.rumford.com on the internet. Traditional fireplaces emit a good amount of radiant heat as well and will perform best if
one complies with the industry standard details provided by the BIA. The third way that fireplace heat can be used is to let the fire heat the air, and then circulate the heated air into the room using a fan.
Several steel inserts are widely available that provide this air circulation effect.
Minimize Stack Loss
It is important to reduce the amount of heated room air lost up the chimney. The most common way to control stack loss is the damper, open when the
fire is burning, and closed immediately after the fire is out. A damper alone is not usually enough to keep air from exiting. The damper closes but most dampers will not be completely airtight. The warm air in the
room will rise due to convection and find it's way through the damper.
Another similar problem is a reverse convection current. This is common when fireplaces are located on the outside of the home. When there is no fire
burning, and the air in the chimney gets cold. A reverse convection current can cause cold air outside to fall down the chimney and into the room. Unwanted odors can be drawn into the room with the air as well.
Glass doors on the fireplace opening can reduce this problem. Dampers placed at the top of the chimney can reduce this problem further, although the air in the flue is still cold and will still "fall" into
the space. Doors and dampers are not completely airtight, but can reduce this affect.
In Conclusion, by maximizing the use of heat, using outside make-up air for combustion, minimize stack loss and adhering to established industry
standards for dimensions and details, one can create an energy efficient fireplace that is more than just decoration.
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