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Designed more for show, traditional open masonry fireplaces should  not be considered heating devices. Traditional fireplaces draw in as much as 300 cubic feet per minute of heated room air for combustion, then send it straight up the chimney. Fireplaces also produce significant air pollution. Although some fireplace designs seek to address these issues with dedicated air supplies, glass doors, and heat recovery systems, fireplaces are still energy losers. When burning a fire, you should turn your heat down or off and open a window near the fireplace. Only high-efficiency fireplace inserts have proven effective in increasing the heating efficiency of older fireplaces. Essentially, the inserts function like woodstoves, fitting into the masonry fireplace or on its hearth, and use the existing chimney. You must install a flue collar that continues from the insert to the top of the chimney. A well-fitted fireplace insert can function nearly as efficiently as a woodstove.
Studies have shown that proper installation of fireplace inserts is very important. Have a professional installer examine the fireplace and chimney to determine if they are suitable for an insert. Inserts should be as airtight as possible. The more airtight it is, the easier it is to control the fire and the heat output. The installer should use only approved fireplace insulating materials to fill any gaps between the fireplace mouth and insert shield. Moving an insert to clean the chimney or liner can be difficult, and is a job best left to a professional chimney sweep. In some situations, a clean-out door can be installed above the insert connection so the insert does not have to be moved as often. Some models have wheels to simplify installation, cleaning, repairs, and other adjustments. Some modern fireplaces heat at efficiencies near those of woodstoves and are certified as low emission appliances. Although designed to include the fire-viewing benefits of a traditional fireplace, this generation of fireplaces can effectively provide heat as well. Through vents under the firebox, room air is drawn in, heated through a heat exchanger, and sent back into the house either through vents at the top of the fireplace or through ducts leading to nearby rooms. Some of these fireplaces are approved to route heated air to a basement auxiliary fan. The air then travels through ducts to other rooms in the house. The fireplace should have a dedicated supply of outside air for combustion. Flues are ideal for leaking heat and warm air out of your home. If you have a fireplace that you don't use, plug and seal the flue. If you use the fireplace, be sure to close the flue when the fireplace is not in use. You could also use an inflatable stopper, available commercially, to temporarily seal the chimney and avoid air leakage through the flue. To improve energy efficiency for an existing home, thermal images from an energy house inspection or home energy audit will reveal many of the leaks in the thermal envelop including around the fireplace. After the review you will have a roadmap to proper weatherization. Whether you are the do it yourself, "DYI" person or want to hand off to a contractor or handyman, the roadmap will help you make the best decision first. Fixing whats found will greatly improve your comfort, savings and reduce your carbon footprint.Article courtesy of the Department of Energy EERE http://www.eere.energy.gov/consumer/your_home/space_heating_cooling/index.cfm/mytopic=12570
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