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A furnace is a device used for high-temperature heating. The name derives from Greek word ''fornax'', which means oven. In American English and Canadian English usage, the term ''furnace'' on its own refers to the household heating systems based on a central furnace (known either as a boiler, or a heater in British English), and sometimes as a synonym for kiln, a device used in the production of ceramics. In British English, a ''furnace'' is an industrial furnace used for many things, such as the extraction of metal from ore (smelting) or in oil refineries and other chemical plants, for example as the heat source for fractional distillation columns. The term ''furnace'' can also refer to a direct fired heater, used in boiler applications in chemical industries or for providing heat to chemical reaction The heat energy to fuel a furnace may be supplied directly by fuel combustion, by electricity such as the electric arc furnace, or through induction heating in induction furnaces. ==Household furnaces== A household furnace is a major appliance that is permanently installed to provide heat to an interior space through intermediary fluid movement, which may be air, steam, or hot water. Heating appliances that use steam or hot water as the fluid are normally referred to as a residential steam boiler or residential hot water boiler. The most common fuel source for modern furnaces in the United States is natural gas; other common fuel sources include LPG (liquefied petroleum gas), fuel oil, coal or wood. In some cases electrical resistance heating is used as the source of heat, especially where the cost of electricity is low. Modern high-efficiency furnaces can be 98% efficient and operate without a chimney. The small amount of waste gas and heat are mechanically ventilated through PVC pipes that can be vented through the side or roof of the house. Fuel efficiency in a gas furnace is measured in AFUE (Annual Fuel Utilization Efficiency). 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Furnace」の詳細全文を読む スポンサード リンク
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