Central heating system

A central heating system provides warmth to the whole interior of a building (or portion of a building) from one point to multiple rooms. When combined with other systems in order to control the building climate, the whole system may be an HVAC (heating, ventilation and air conditioning) system.

Central heating differs from space heating in that the heat generation occurs in one place, such as a furnace room or basement in a house or a mechanical room in a large building (though not necessarily at the geometrically "central" point). The heat is distributed throughout the building, typically by forced-air through ductwork, by water circulating through pipes, or by steam fed through pipes. The most common method of heat generation involves the combustion of fossil fuel in a furnace or boiler.

In much of the temperate climate zone, most detached housing has had central heating installed since before the Second World War. Where coal was readily available (i.e. the Anthracite coal region in northeast Pennsylvania) coal-fired steam or hot water systems were common. In more recent times, these have been updated to use fuel oil or gas as the source of combustion, eliminating the need for a large coal storage bin near the boiler and the need to remove and discard ashes after the coal is burned. Coal-fired systems are now mostly reserved for larger buildings.

A cheaper alternative to hot water or steam heat is forced hot air. A furnace burns fuel oil, which heats air in a heat exchanger, and blower fans circulate the warmed air through a network of ducts to the rooms in the building. This system is cheaper because the air moves through a series of ducts instead of pipes, and does not require a pipe fitter to install. The space between floor joists can be boxed in and used as some of the ductwork, further lowering costs.

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