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1. A furnace is a device used for heating.
In American English, the term furnace on its own is generally used to describe 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 to fire clay to produce ceramics.
In British English the term furnace is used exclusively to mean industrial furnaces which are 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.
Unique furnaces are used to run fire tests to qualify fire protection products for use in construction.
The heat energy to fuel a furnace may be supplied directly by combustion of some fuel, or electric furnaces such as the electric arc furnace or induction furnace use remotely generated electric power.
2.Almost 35 million homes in America are heated by natural gas-fired forced-air heating systems, by far the most popular form of central heating. Unfortunately, nearly all of these households have been sending 30% or more of their energy dollars up the furnace flue and, in doing so, each has pumped up to four tons of carbon dioxide, the "greenhouse gas," into the atmosphere every month. Most conventional forced-air furnaces operate at very low efficiencies -- some taking advantage of only half the fuel they burn.
In an effort to curb this waste and pollution, the U.S. Department of Energy (DOE) instituted rigid new standards at the beginning of 1992 that require every new furnace to turn at least 78% of its fuel into heat. Manufacturers have responded with models that, at the minimum, meet this standard and, at best, far surpass it.
3.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. 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.
Combustion furnaces always need to be vented to the outside. Traditionally, this was through a chimney, which tends to expel heat along with the exhaust. Modern high-efficiency furnaces can be 98% efficient and operate without a chimney. The small amount of waste gas and heat are mechanically ventillated through a small tube through the side or roof of the house.
* "High-efficiency" in this sense may be misleading, because furnace efficiency is typically expressed as a "first-law" efficiency, whereas the exergy efficiency of a typical furnace is much lower than the first-law thermal efficiency. By comparison, cogeneration has a higher exergy efficiency than is realizable from burning fuel to generate heat directly at a moderate temperature. However, as the vast majority of consumers (as well as many government regulators) are unfamiliar with exergy efficiency, Carnot efficiency, and the Second Law of Thermodynamics, the use of first-law efficiencies to rate furnaces is well-entrenched.
Modern household furnaces are classified as condensing or non-condensing based on their efficiency in extracting heat from the exhaust gases. Furnaces with efficiencies greater than approximately 89% extract so much heat from the exhaust that water vapor in the exhaust condenses; they are referred to as condensing furnaces. Such furnaces must be designed to avoid the corrosion that this highly acidic condensate might cause and may need to include a condensate pump to remove the accumulated water. Condensing furnaces can typically deliver heating savings of 20%-35% assuming the old furnace was in the 60% Annual Fuel Utilization Efficiency (AFUE) range.
4. Metallurgical furnaces
In metallurgy, several specialised furnaces are used. These include:
* Furnaces used in smelters, including:
o The blast furnace, used to reduce iron ore to pig iron
o Steelmaking furnaces, including:
+ Puddling furnace
+ Reverberatory furnace
+ Bessemer converter
+ Open hearth furnace
+ Basic oxygen furnace
+ Electric arc furnace
+ Electric induction furnace
* Furnaces used to remelt metal in foundries.
* Furnaces used to reheat and heat treat metal for use in:
o Rolling mills, including tinplate works and slitting mills.
o Forges.
* Vacuum furnaces
5.A new, high-efficiency furnace can save you money in the long run, so if your furnace needs replacement, it pays to get a new high-efficiency model. But does your furnace need replacement. Do you want a new furnace because your present one isn't heating properly or is making too much noise? You may find that simple repairs are all that's needed. If you're considering a new furnace to eliminate problems with an older one, first read through these common problems and their fixes--this information just might save you a bundle.
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