Furnace (central heating)
Furnace Categories:
– Natural draft furnaces:
– Used cast-iron or steel heat exchangers within brick or masonry shells.
– Required daily maintenance for solid fuels.
– Adapted over time with electric blowers for better heat distribution.
– Forced-air furnaces:
– Replaced natural draft systems in the 1950s and 1960s.
– Moved heated air with blowers on various speeds.
– Achieved energy efficiency ranging from 50% to over 65% AFUE.
– Forced draft furnaces:
– More compact with steel heat exchangers.
– Equipped with combustion air blowers for increased fuel efficiency.
– Compatible with central air-conditioning systems.
– Condensing furnaces:
– Achieved high efficiency between 90% and 98% AFUE.
– Captured latent heat from exhaust gases for improved efficiency.
– Utilized sealed combustion areas and secondary heat exchangers.
Heat Distribution Methods:
– Furnace transfers heat to living spaces through distribution systems.
– Boilers provide hot water for bathing and washing dishes.
– Air convection systems use passive air circulation for heat distribution.
– Modern warm air furnaces use fans for forced-air heat.
– Ductwork can be made of sheet metal or plastic flex duct.
Additional Resources:
– Practical Heating Technology by Johnson & Standiford.
– Encyclopedia Britannica entry on Furnace.
– US Dept. of Energy resources on furnaces and boilers.
– Handbook on Single, Multi & Variable Speed Furnaces by Ahmed.
– Green Leaf Air’s information on furnace technology.
Related Topics:
– Phase-out of gas boilers.
– Condensing boiler.
– Forced-air gas.
– Jetstream furnace.
– Outdoor wood-fired boiler.
References:
– Wikimedia Commons has media related to Furnace.
– Engineering calculations in radiative heat transfer by Gray & Muller.
– Fundamentals of radiation heat transfer by Fiveland et al.
– Handbook of valves, piping, and pipelines by Warring.
– Improving boiler efficiency by Dukelow.
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A furnace (American English), referred to as a heater or boiler in British English, is an appliance used to generate heat for all or part of a building. Furnaces are mostly used as a major component of a central heating system. Furnaces are 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 boilers or residential hot water boilers. The most common fuel source for modern furnaces in North America and much of Europe is natural gas; other common fuel sources include LPG (liquefied petroleum gas), fuel oil, wood and in rare cases coal. In some areas electrical resistance heating is used, especially where the cost of electricity is low or the primary purpose is for air conditioning. Modern high-efficiency furnaces can be up to 98% efficient and operate without a chimney, with a typical gas furnace being about 80% efficient. Waste gas and heat are mechanically ventilated through either metal flue pipes or polyvinyl chloride (PVC) pipes that can be vented through the side or roof of the structure. Fuel efficiency in a gas furnace is measured in AFUE (Annual Fuel Utilization Efficiency).
