Using fireplaces efficiently
Tips and products to help you get the most from a fireplaceBy James Dulley
That cozy open fire may actually be costing you a lot of money. First, there’s the cost of firewood if you don’t cut your own. Second, the radiant heat feels nice when you are right in front of the fire, but already-heated air might be sucked up the chimney if outside combustion air is not introduced at the fire. This makes your heating system run longer as it replaces already heated air from your furnace or heat pump.
Also, if there is no damper or the fireplace is not fitted with its own outdoor air source, indoor air escapes up the chimney when the fireplace is not used.
Adding a source of combustion air that ducts into the fireplace can help a great deal — and this works well in combustion with glass doors. The fire draws the air it needs for proper combustion and draft from the outside, rather than the conditioned air from inside.
If you don’t have an outdoor vent in your fireplace or stove, it helps to open a window by the fireplace a little and close doors to the room if possible. Much of the excess air being drawn up the chimney will be cold outdoor air from the slightly open window. When sitting right in front of the hot fire, you probably won’t notice the air draft caused by the open window.
If you make just one fireplace efficiency investment, it should be to install high-quality glass doors. They control the amount of indoor air that escapes up the chimney when a fire is burning, and also when one is not.
High-quality fireplace doors aren’t cheap. The best are relatively airtight. By adjusting combustion air vents in the bottom of the glass door frame, you can still have a raging fire without major indoor air loss.
Fire does need an adequate supply of combustion air for an efficient, clean burn. If air flow is reduced too much, creosote buildup occurs, leaving the potential for a chimney fire. Have the chimney inspected annually and apply several squirts of a creosote control spray during each fire.
Burn well-seasoned wood only or no more than one unseasoned log to three seasoned ones. If you try to burn more unseasoned wood, it requires more combustion air to keep it burning well, which can draw even more air out of your home.
There are several designs of heat-circulating grates that increase heat output. Many efficient grates fit snugly under the bottom edge of the fireplace doors and contain an electric blower that circulates indoor air through the grate, keeping the room air warm.
If you decide to purchase a heat-circulating grate, select one with a blower with several speeds and a thermostat with an on/off switch. This switch shuts off the blower when the fire burns down. If you prefer the fireplace doors open, tubular heat-circulating grates blow the heat directly out the front. Other models have no blower and rely on natural convection.
Stoll Fireplace makes a unique heat exchanger, which mounts at the top of the fireplace opening, creating a tremendous amount of heat output. These models work with gas or wood-burning fireplaces. A circulating heat exchanger with built-in glass doors is also available for a more airtight combination. Also, an optional upper oven section is available for cooking and baking, which can help reduce energy use.
For more about fireplace efficiency, check out TogetherWeSave.com’s Home Efficiency Analysis Tool (homeefficiency.togetherwesave.com).