About Furnaces
A furnace, or boiler, is a device for heating a home or other building. Furnaces can run on electricity, wood, gas or oil. Furnaces operate by distributing heated air through ducts. Boilers, in contrast, operate by circulating hot water through pipes to radiators in each room. All furnaces have efficiency ratings that tell you how well fuel is utilized by your furnace. Does this Spark an idea?
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Operation
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No matter what type of fuel that is used, all furnaces work the same way. Air is drawn into the furnace, where it passes over a heat exchange unit and is heated. Waste gases are vented out of a chimney. The warm air is then forced out into ducts and spreads throughout the house or other building. Since warm air rises, most furnaces are located in basements or on the ground floor. Forced air furnaces use fans to blow the air throughout the building, heating the rooms quickly. A gravity furnace allows the air to circulate naturally. This is slower but quieter.
Types
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There are several different types of furnaces in general use. The most common is the central warm air furnace that heats air then distributes it through ducts. Steam or hot water furnaces, or boilers, heat water and then distribute it around the building via pipes. Water then circulates around radiators in each room, which heat the air around them. Other hot water furnaces distribute hot water to pipes in the floor, which heat the floor. The warm air then rises from the floor, heating the rooms. A heat pump uses a compressor and a heating coil to distribute heat around a building via ducts. A pipeless furnace delivers radiated heat to the rooms directly above or next to the furnace.
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Efficiency Ratings
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The fuel efficiency of a furnace is measured by its annual fuel utilization efficiency (AFUE). This is a measure of the heat given out compared to the energy consumed over the course of a typical year. An AFUE of 80 percent means that 80 percent of the fuel used is turned into heat for your home while the remaining 20 percent is wasted. This figure does not include heat lost to ducts or pipes. The Federal Trade Commission requires a minimum AFUE of 78 percent for fossil-fueled, warm air furnaces, a minimum AFUE of 80 percent for fossil fuel boilers and a minimum AFUE of 75 percent for gas-fueled boilers. Electric furnaces are the most efficient, with an AFUE of between 95 and 100 percent.
System Efficiency
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The equipment used in a furnace can have a big effect on its efficiency. Low efficiency furnaces tend to rely on natural air flow to circulate air over the heater and have a pilot light that is always on. Mid-efficiency furnaces use an exhaust fan to control the flow of air over the heat exchanger more precisely and an electronic ignition that uses less fuel. These furnaces may also direct air through a smaller diameter pipe -- this speeds up heating, and less fuel is used. High-efficiency furnaces may run the air through a second heat exchanger and use a sealed combination chamber to prevent loss of heat from the system. Efficiency can also be improved by using a furnace that is exactly the right size for your property so that you are not creating heat you don't need.
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References
- Photo Credit chimney image by kenmo from Fotolia.com
