The majority of homes built in the United States are built with some sort of wood burning or gas fireplace. As we look at making our homes and fireplaces more efficient in the use of energy, it is necessary to take a look at the current fireplace design practices to determine what we should change or do to get the most out of our fireplaces. So, let's take a look at some of the ways of increasing the heating potential of masonry fireplaces.

When we talk about whether or not a fireplace is energy efficient, let's look at three questions that will greatly effect the energy efficiency:
Where does the air that feeds the fire come from? inside or outside?
How can we reduce the amount of heat lost up the chimney? (stack loss)
How can we maximize the amount of heat that actually enters the room?

1. Where does the air that feeds the fire come from? inside or outside?
Fires need air to fuel them, and the air that fuels a fire has to come from somewhere. Today homes are airtight, and air only enters at prescribed locations. Homes are a controlled environment, so the air that comes into a furnace, for example, is heated and distributed throughout the home.

With a fireplace, air is drawn into the firebox to be consumed in the fire, and then is expelled up the flue and out of the house. For the most part, in a cold environment, the air drawn into the firebox comes from the house and has already been heated to a comfortable temperature by the central heating system. As the air is expelled up the flue, it has to be replaced by more air.

So, where does this air come from in the first place? It must come into the house from the outside, be heated up by the central heating, and then fuel the fire. Obviously, this process uses a lot of energy. A source of outside air must be provided. In houses with a forced air heating system, the make-up air can be provided through a fresh air duct connected to the cold air return. If you are lacking such a system your fireplace will not be energy efficient; thus, it should be remedied. This means that an outside air supply should be built into the fireplace itself to increase efficiency. The intake should be located on an exterior wall or on the back of the fireplace. It should have a screen backed, closeable louver that can be operated from the inside. The intake should be high enough above grade to avoid snow blockage, because if it gets covered by snow it becomes worthless.

2. How can we reduce the amount of heat lost up the chimney? (stack loss)
The most common way to control stack loss is through the damper; keep it open when the fire is burning, and closed immediately after the fire is out. However, a damper alone is not usually enough to keep air from exiting. Although the damper closes, most dampers are not completely airtight. The warm air in the room will rise due to convection and find it's way through the damper. So, try to make your damper as airtight as possible, and be sure to close it so you do not lose your hot air through it.

3. How can we maximize the amount of heat that actually enters the room?
There are several ways to maximize the heat created by a fire: one is to provide a masonry mass that absorbs, stores, and slowly re-radiates heat energy back into the room. This provides a slow, low intensity heat source long after the fire is out. Another thing you can do is position the fireplace wholly within the home. This will make your fireplace 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. Last you can circulate the heated air into the room using a fan. Several steel inserts are widely available that provide this air circulation effect.

So, 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.