Furnace - wikipedia Furnace For other uses, see Furnace ( disambiguation ). This article has multiple issues. Please help improve it or discuss these issues on the talk page. ( Learn how and when to remove these template messages ) This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. ( July 2007 ) 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. ( April 2014 ) Industrial furnace from 1907. 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. 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 reactions for processes like cracking, and is part of the standard English names for many metallurgical furnaces worldwide. Contents 1 Categories 1.1 Natural draft 1.2 Forced - air 1.3 Forced draft 1.4 Condensing 1.5 Furnace types 1.5. 1 Single - stage 1.5. 2 Two - stage 1.5. 3 Modulating 2 Heat distribution 3 Home furnaces 4 Metallurgical furnaces 5 Industrial furnaces 6 See also 7 Notes 8 References 9 External links Categories Furnaces can be classified into four general categories, based on efficiency and design. Natural draft 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. These furnaces could be made to work with any fuel simply by adapting the burner area. They have been operated with wood, coke, coal, trash, paper, natural gas, and fuel oil. Furnaces that used solid fuels required daily maintenance to remove ash and `` clinkers '' that accumulated in the bottom of the burner area. In later years, these furnaces were adapted with electric blowers to aid air distribution and speed moving heat into the home. Gas and oil - fired systems were usually controlled by a thermostat inside the home, while most wood and coal - fired furnaces had no electrical connection and were controlled by the amount of fuel in the burner and position of the fresh - air damper on the burner access door. Forced - air The second category of furnace is the forced - air, atmospheric burner style with a cast - iron or sectional steel heat exchanger. Through the 1950s and 1960s, this style of furnace was used to replace the big, natural draft systems, and was sometimes installed on the existing gravity duct work. The heated air was moved by blowers which were belt driven and designed for a wide range of speeds. These furnaces were still big and bulky compared to modern furnaces, and had heavy - steel exteriors with bolt - on removable panels. Energy efficiency would range anywhere from just over 50 % to upward of 65 % AFUE. This style furnace still used large, masonry or brick chimneys for flues and was eventually designed to accommodate air - conditioning systems. Forced draft The third category of furnace is the forced draft, mid-efficiency furnace with a steel heat exchanger and multi-speed blower. These furnaces were physically much more compact than the previous styles. They were equipped with combustion air blowers that would pull air through the heat exchanger which greatly increased fuel efficiency while allowing the heat exchangers to become smaller. These furnaces may have multi-speed blowers and were designed to work with central air - conditioning systems. A condensing furnace Condensing The fourth category of furnace is the high - efficiency, or condensing furnace. High - efficiency furnaces can achieve from 89 % to 98 % fuel efficiency. This style of furnace includes a sealed combustion area, combustion draft inducer and a secondary heat exchanger. Because the heat exchanger removes most of the heat from the exhaust gas, it actually condenses water vapor and other chemicals ( which form a mild acid ) as it operates. The vent pipes are normally installed with PVC pipe versus metal vent pipe to prevent corrosion. The draft inducer allows for the exhaust piping to be routed vertically or horizontally as it exits the structure. The most efficient arrangement for high - efficiency furnaces include PVC piping that brings fresh combustion air from the outside of the home directly to the furnace. Normally the combustion air ( fresh air ) PVC is routed alongside the exhaust PVC during installation and the pipes exit through a sidewall of the home in the same location. High efficiency furnaces typically deliver a 25 % to 35 % fuel savings over a 60 % AFUE furnace. Furnace types Single - stage A single - stage furnace has only one stage of operation, it is either on or off. This means that it is relatively noisy, always running at the highest speed, and always pumping out the hottest air at the highest velocity. One of the benefits to a single - stage furnace is typically the cost for installation. Single - stage furnaces are relatively inexpensive since the technology is rather simple. Two - stage This type has two stages of operation, full speed and half ( or reduced ) speed. Depending on the demanded heat, they can run at a lower speed most of the time. They can be quieter, move the air at less velocity, and will better keep the desired temperature in the house. Modulating This type of furnace can modulate the heat output and air velocity nearly continuously, depending on the demanded heat and outside temperature. This means that it only works as much as necessary and therefore saves energy. Heat distribution The furnace transfers heat to the living space of the building through an intermediary distribution system. If the distribution is through hot water ( or other fluid ) or through steam, then the furnace is more commonly called a boiler. One advantage of a boiler is that the furnace can provide hot water for bathing and washing dishes, rather than requiring a separate water heater. One disadvantage to this type of application is when the boiler breaks down, neither heating nor domestic hot water are available. `` Octopus '' furnace with oil burner. Air convection heating systems have been in use for over a century. Older systems rely on a passive air circulation system where the greater density of cooler air causes it to sink into the furnace area below, through air return registers in the floor, and the lesser density of warmed air causes it to rise in the ductwork ; the two forces acting together to drive air circulation in a system termed ' gravity - fed '. The layout of these ' octopus ' furnaces and their duct systems is optimized with various diameters of large dampered ducts. Forced - air gas furnace, design circa 1991. By comparison, most modern `` warm air '' furnaces typically use a fan to circulate air to the rooms of house and pull cooler air back to the furnace for reheating ; this is called forced - air heat. Because the fan easily overcomes the resistance of the ductwork, the arrangement of ducts can be far more flexible than the octopus of old. In American practice, separate ducts collect cool air to be returned to the furnace. At the furnace, cool air passes into the furnace, usually through an air filter, through the blower, then through the heat exchanger of the furnace, whence it is blown throughout the building. One major advantage of this type of system is that it also enables easy installation of central air conditioning, simply by adding a cooling coil at the outlet of the furnace. Air is circulated through ductwork, which may be made of sheet metal or plastic `` flex '' duct, and is insulated or uninsulated. Unless the ducts and plenum have been sealed using mastic or foil duct tape, the ductwork is likely to have a high leakage of conditioned air, possibly into unconditioned spaces. Another cause of wasted energy is the installation of ductwork in unheated areas, such as attics and crawl spaces ; or ductwork of air conditioning systems in attics in warm climates. Home furnaces Main article : Central heating A home 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 North America and much of Europe is natural gas ; other common fuel sources include LPG ( liquefied petroleum gas ), fuel oil and in rare cases coal or wood. 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 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 ). Metallurgical furnaces The Manufacture of Iron -- Filling the Furnace, an 1873 wood engraving In metallurgy, several specialized furnaces are used. These include : Furnaces used in smelters, including : The blast furnace, used to reduce iron ore to pig iron Steelmaking furnaces, including : Puddling furnace Reverberatory furnace Bessemer converter Open hearth furnace Basic oxygen furnace Electric arc furnace Electric induction furnace Reheating furnace Furnaces used to remelt metal in foundries. Furnaces used to reheat and heat treat metal for use in : Rolling mills, including tinplate works and slitting mills. Forges. Vacuum furnaces Industrial furnaces Main article : Industrial furnace Schematic diagram of an industrial process furnace An industrial furnace or direct fired heater, is an equipment used to provide heat for a process or can serve as reactor which provides heats of reaction. Furnace designs vary as to its function, heating duty, type of fuel and method of introducing combustion air. However, most process furnaces have some common features. Fuel flows into the burner and is burnt with air provided from an air blower. There can be more than one burner in a particular furnace which can be arranged in cells which heat a particular set of tubes. Burners can also be floor mounted, wall mounted or roof mounted depending on design. The flames heat up the tubes, which in turn heat the fluid inside in the first part of the furnace known as the radiant section or firebox. In this chamber where combustion takes place, the heat is transferred mainly by radiation to tubes around the fire in the chamber. See also Basic oxygen steelmaking Batch oven Blast furnace Cremation Electric arc furnace Fan heater Fire test furnaces Forced - air gas Geothermal heat pump ( Geothermal systems ) HVAC Industrial furnace Jetstream furnace Masonry heater Open hearth furnace Russian oven Shell boiler Solar power Notes ^ Homebuilding, Fine ( 2017 - 05 - 09 ). Home Repair Wisdom & Know - How : Timeless Techniques to Fix, Maintain, and Improve Your Home. Hachette Books. ISBN 9780316362887. ^ Johnson, Bill ; Standiford, Kevin ( 2008 - 08 - 28 ). Practical Heating Technology. Cengage Learning. p. 116. ISBN 141808039X. References Gray, W.A. ; Muller, R ( 1974 ). Engineering calculations in radiative heat transfer ( 1st ed. ). Pergamon Press Ltd. ISBN 0 - 08 - 017786 - 7. Fiveland, W.A., Crosbie, A.L., Smith A.M. and Smith, T.F. ( Editors ) ( 1991 ). Fundamentals of radiation heat transfer. American Society of Mechanical Engineers. ISBN 0 - 7918 - 0729 - 0. CS1 maint : Multiple names : authors list ( link ) CS1 maint : Extra text : authors list ( link ) Warring, R. H ( 1982 ). Handbook of valves, piping and pipelines ( 1st ed. ). Gulf Publishing Company. ISBN 0 - 87201 - 885 - 7. Dukelow, Samuel G ( 1985 ). Improving boiler efficiency ( 2nd ed. ). Instrument Society of America. ISBN 0 - 87664 - 852 - 9. Whitehouse, R.C. ( Editor ) ( 1993 ). The valve and actuator user 's manual. Mechanical Engineering Publications. ISBN 0 - 85298 - 805 - 2. CS1 maint : Extra text : authors list ( link ) Davies, Clive ( 1970 ). Calculations in furnace technology ( 1st ed. ). Pergamon Press. ISBN 0 - 08 - 013366 - 5. Goldstick, R. ; Thumann, A ( 1986 ). Principles of waste heat recovery. Fairmont Press. ISBN 0 - 88173 - 015 - 7. ASHRAE ( 1992 ). ASHRAE Handbook. Heating, ventilating and air - conditioning systems and equipment. ASHRAE. ISBN 0 - 910110 - 80 - 8. ISSN 1078 - 6066. Perry, R.H. and Green, D.W. ( Editors ) ( 1997 ). Perry 's Chemical Engineers ' Handbook ( 7th ed. ). McGraw - Hill. ISBN 0 - 07 - 049841 - 5. CS1 maint : Multiple names : authors list ( link ) CS1 maint : Extra text : authors list ( link ) Lieberman, P. ; Lieberman, Elizabeth T ( 2003 ). Working Guide to Process Equipment ( 2nd ed. ). McGraw - Hill. ISBN 0 - 07 - 139087 - 1. External links Wikimedia Commons has media related to Furnace. Furnaces, Incinerators, Kilns at DMOZ https://www.youtube.com/ How It Works : Furnace Heating, ventilation and air conditioning Fundamental concepts Air changes per hour Bake - out Building envelope Convection Dilution Domestic energy consumption Enthalpy Fluid dynamics Gas compressor Heat pump and refrigeration cycle Heat transfer Humidity Infiltration Latent heat Noise control Outgassing Particulates Psychrometrics Sensible heat Stack effect Thermal comfort Thermal destratification Thermal mass Thermodynamics Vapour pressure of water Technology Absorption refrigerator Air barrier Air conditioning Antifreeze Automobile air conditioning Autonomous building Building insulation materials Central heating Central solar heating Chilled beam Chilled water Constant air volume ( CAV ) Coolant Dedicated outdoor air system ( DOAS ) Deep water source cooling Demand - controlled ventilation ( DCV ) Displacement ventilation District cooling District heating Electric heating Energy recovery ventilation ( ERV ) Firestop Forced - air Forced - air gas Free cooling Heat recovery ventilation ( HRV ) Hybrid heat Hydronics HVAC Ice storage air conditioning Kitchen ventilation Mixed - mode ventilation Microgeneration Natural ventilation Passive cooling Passive house Radiant heating and cooling system Radiant cooling Radiant heating Radon mitigation Refrigeration Renewable heat Room air distribution Solar air heat Solar combisystem Solar cooling Solar heating Thermal insulation Underfloor air distribution Underfloor heating Vapor barrier Vapor - compression refrigeration ( VCRS ) Variable air volume ( VAV ) Variable refrigerant flow ( VRF ) Ventilation Components Air conditioner inverter Air door Air filter Air handler Air ionizer Air - mixing plenum Air purifier Air source heat pumps Automatic balancing valve Back boiler Barrier pipe Blast damper Boiler Centrifugal fan Chiller Condensate pump Condenser Condensing boiler Convection heater Cooling tower Damper Dehumidifier Duct Economizer Electrostatic precipitator Evaporative cooler Evaporator Exhaust hood Expansion tank Fan coil unit Fan heater Fire damper Fireplace Fireplace insert Freeze stat Flue Freon Fume hood Furnace Furnace room Gas compressor Gas heater Gasoline heater Geothermal heat pump Grease duct Grille Ground - coupled heat exchanger Heat exchanger Heat pipe Heat pump Heating film Heating system High efficiency glandless circulating pump High - efficiency particulate air ( HEPA ) High pressure cut off switch Humidifier Infrared heater Inverter compressor Kerosene heater Louver Mechanical fan Mechanical room Oil heater Packaged terminal air conditioner Plenum space Pressurisation ductwork Process duct work Radiator Radiator reflector Recuperator Refrigerant Register Reversing valve Run - around coil Scroll compressor Solar chimney Solar - assisted heat pump Space heater Smoke exhaust ductwork Thermal expansion valve Thermal wheel Thermosiphon Thermostatic radiator valve Trickle vent Trombe wall Turning vanes Ultra-low particulate air ( ULPA ) Whole - house fan Windcatcher Wood - burning stove Measurement and control Air flow meter Aquastat BACnet Blower door Building automation Carbon dioxide sensor Clean Air Delivery Rate ( CADR ) Gas sensor Home energy monitor Humidistat HVAC control system Intelligent buildings LonWorks Minimum efficiency reporting value ( MERV ) OpenTherm Programmable communicating thermostat Programmable thermostat Psychrometrics Room temperature Smart thermostat Thermostat Thermostatic radiator valve Professions, trades, and services Architectural acoustics Architectural engineering Architectural technologist Building services engineering Building information modeling ( BIM ) Deep energy retrofit Duct leakage testing Environmental engineering Hydronic balancing Kitchen exhaust cleaning Mechanical engineering Mechanical, electrical, and plumbing Mold growth, assessment, and remediation Refrigerant reclamation Testing, adjusting, balancing Industry organizations ACCA AMCA ASHRAE ASTM International BRE BSRIA CIBSE LEED SMACNA Health and safety Indoor air quality ( IAQ ) Passive smoking Sick building syndrome ( SBS ) Volatile organic compound ( VOC ) See also ASHRAE Handbook Building science Fireproofing Glossary of HVAC terms Template : Home automation Template : Solar energy Retrieved from `` https://en.wikipedia.org/w/index.php?title=Furnace&oldid=797324676 '' Categories : Fireplaces Residential heating appliances Industrial furnaces Industrial processes Inventions of the Indus Valley Civilisation Hidden categories : Articles needing additional references from July 2007 All articles needing additional references Articles lacking in - text citations from April 2014 All articles lacking in - text citations CS1 maint : Multiple names : authors list CS1 maint : Extra text : authors list Articles with DMOZ links Talk Contents About Wikipedia Български Cymraeg Ελληνικά Español فارسی Français हिन्दी Ido Bahasa Indonesia Italiano עברית 日本 語 Русский Simple English Slovenščina Svenska தமிழ் Українська Vepsän kel ' 文言 中文 Edit links This page was last edited on 26 August 2017, at 09 : 33. 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Question: heat exchangers in gas fired furnaces are made of
Answer: cast-iron or riveted-steel