Q: We want an efficient wood-burning fireplace/insert for extra heat and emergencies. Our old masonry fireplace seems to chill the house. What should we look for?
A: It is not just your imagination. Using an open masonry fireplace can cool your house and result in higher overall heating costs. Heated indoor air is drawn into the fireplace opening and lost up the chimney. This draws cold outdoor air into your house through windows, doors and gap.
You may feel comfortable by the fireplace, but your heat pump or furnace can run up to 10 percent more to warm the rest of the house.
I do not recommend using an open fireplace during very cold weather, but if you really like the ambiance of a fire, close all the doors to that room and crack open a window. Some heated air will still be lost up the chimney from the rest of the house, but most of this air will be drawn in the open window. The loss is not as severe during mild weather because the outdoor air leaking in is not as cold.
Burning firewood to heat your home is called biomass heating and it may qualify for some local tax credits. Biomass includes cord firewood, wood pellets, corn, switch grass, peanut shells and cherry pits. It can be burned in a variety of heating appliances. Fireplaces, wood and pellet stoves are most common. If you plan to burn corn, be sure to get a model with a firepot designed to handle corn’s unique burning characteristics.
Every efficient wood-burning fireplace or insert has tight-sealing glass doors to minimize the loss of already-heated room air. Some fireplace models can be safely operated with the glass doors opened and just a screen covering the opening. Do not burn it this way often because too much indoor air is lost.
There are many sizes and styles available. A 42-inch wide, EPA-certified wood-burning fireplace can produce from 8,000 to 60,000 British thermal units an hour depending on how much wood is in the firebox. The overall efficiency can be as high as high as 77 percent. A fireplace this size can handle logs up to 22 inches long.
If you decide on a fireplace, you must decide between a zero-clearance and a masonry fireplace. If your old fireplace is large, you may be able to fit a new insert
inside of it, saving hundreds of dollars. If you plan to install a fireplace somewhere else, installing a zero-clearance model is best. These use a double-walled design with insulation to be safely placed against wood wall studs.
A heating-circulating type of fireplace is a must for the best efficiency and more heated air output. Many designs operate without a fan and rely on natural flow of room air around the superhot firebox. As the air gets hot, it becomes less dense and naturally flows out into the room through an upper vent. This pulls cooler room air in a lower inlet to be heated.
For more heat output and better control of the flow of heated air, install an optional blower kit. The better ones have thermostats and variable-speed controls for the best comfort. Select one with at least 100 cubic feet per minute air flow. Each fireplace manufacturer offers its own specially designed blower kit. A blower kit can usually be added by the homeowner after the fireplace is installed.
For the greatest efficiency and fewest drafts indoors, install an outdoor combustion air kit with the fireplace. Make this decision before you install the fireplace because a duct has to run to it to bring in the outdoor air. Installation is simpler with a raised hearth design.
Another efficient option is an airtight insert. These provide the longest burn time and maximum heat output. They typically are not as stylish as other fireplaces, but they provide much better control over the heat output and combustion air used. For air quality considerations, select one that is EPA certified. Pellet and catalytic cord firewood models typically produce the least particulate matter.