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This article includes a list of references, but its sources remain unclear because it has insufficient inline citations. Please help to improve this article by introducing more precise citations. A furnace is a device used for high-temperature heating.
The name derives from Greek word fornax, which means oven. 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. In American English and Canadian English usage, the term furnace refers to the household heating systems based upon a central furnace, otherwise known either as a boiler, or a heater in British English. Furnace may also be a synonym for kiln, a device used in the production of ceramics.
The term furnace can also refer to a direct fired heater, used in boiler applications in chemical industries or for providing heat to chemical reactions for processes like cracking, and is part of the standard English names for many metallurgical furnaces worldwide. Furnaces can be classified into four general categories, based on efficiency and design. Diagram of natural draft gas furnace, early 20th century.
The first category of furnaces are natural draft, atmospheric burner furnaces. These furnaces consisted of cast-iron or riveted-steel heat exchangers built within an outer shell of brick, masonry, or steel. The heat exchangers were vented through brick or masonry chimneys.
Air circulation depended on large, upwardly pitched pipes constructed of wood or metal. The pipes would channel the warm air into floor or wall vents inside the home. This method of heating worked because warm air rises. The system was simple, had few controls, a single automatic gas valve, and no blower.