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Stove
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A stove is an enclosed heated space. The term is commonly taken to mean an enclosed space in which fuel is burned to provide heating, either to heat the space in which the stove is situated or to heat the stove itself, and items placed on it, for cooking purposes. This article is principally concerned with enclosed stoves burning solid fuels for room heating.
osed stoves hold out the possibility of greater efficiency, controllability and lower smoke emission than simple open fires.
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Encyclopedia
A stove is an enclosed heated space. The term is commonly taken to mean an enclosed space in which fuel is burned to provide heating, either to heat the space in which the stove is situated or to heat the stove itself, and items placed on it, for cooking purposes. This article is principally concerned with enclosed stoves burning solid fuels for room heating.
Efficiency
Enclosed stoves hold out the possibility of greater efficiency, controllability and lower smoke emission than simple open fires. In free air solid fuels burn at a temperature of only about 270°C, too low a temperature for perfect combustion reactions to occur, heat produced through convection is largely lost, smoke particles are evolved without being fully burned and the supply of combustion air cannot be readily controlled.
By enclosing the fire in a chamber and connecting it to a chimney draft (draught) is generated pulling fresh air through the burning fuel. This causes the temperature of combustion to rise to a point (c600°C) where efficient combustion is achieved, the enclosure allows the ingress of air to be regulated and losses by convection are almost eliminated. It also becomes possible, with ingenious design, to direct the flow of burned gasses inside the stove such that smoke particles are heated and destroyed.
Enclosing a fire also prevents heated air from being sucked from the room into the chimney. This can represent a significant loss of heat as an open fireplace can pull away many cubic metres of heated air per hour.
A first step in improvement was the fire chamber: the fire was enclosed on three sides by brick-and-mortar walls and covered by an iron plate. Only in 1735 did the first design that completely enclosed the fire appear: the Castrol stove of the French architect François Cuvilliés was a masonry construction with several fireholes covered by perforated iron plates. It is also known as a stew stove. Near the end of the 18th century, the design was refined by hanging the pots in holes through the top iron plate, thus improving heat efficiency even more.
In 1742 Benjamin Franklin patented an all-metal stove with folding doors.
Some stoves use a catalytic converter which causes combustion of the gas and smoke particles not previously burned. Other models use a design that includes firebox insulation, a large baffle to produce a longer, hotter gas flow path. Modern enclosed stoves are often built with a window to let out some light and to enable the user to view progress of the fire.
While enclosed stoves are typically more efficient and controllable than open fires, there are exceptions. The type of water-heating 'back boiler' open fires commonly used in Ireland, for instance, can be more than 80% absolute efficiency, while the type of enclosed stove commonly used in China may be less than 15% efficient.
Material
Masonry heaters were developed to control air flow in stoves. A masonry heater is designed to allow complete combustion by burning fuels at full-temperature with no restriction of air inflow. Due to its large thermal mass the captured heat is radiated over long periods of time without the need of constant firing, and the surface temperature is generally not dangerous to touch.
Metal stoves came into use in the 18th century. An early, and famous, example of a metal stove is the Franklin stove, said to have been invented by Benjamin Franklin in 1742. It had a labyrinthine path for hot exhaust gases to escape, thus allowing heat to enter the room instead of going up the chimney. The Franklin stove, however, was designed for heating, not for cooking. Benjamin Thompson at the turn to the 19th century was among the first to present a working metal kitchen stove. His Rumford fireplace used one fire to heat several pots that were also hung into holes so that they could be heated from the sides, too. It was even possible to regulate the heat individually for each hole. His stove was designed for large canteen or castle kitchens, though. It would take another 30 years until the technology had been refined and the size of the iron stove been reduced enough for domestic use. Philo Stewart's Oberlin stove was a much more compact, wood-burning cast-iron stove, patented in the U.S. in 1834. It became a huge commercial success with some 90,000 units sold in the next 30 years. In Europe, similar designs also appeared in the 1830s. In the following years, these iron stoves evolved into specialised cooking appliances with flue pipes connected to the chimney, oven holes, and installations for heating water. The originally open holes into which the pots were hung were now covered with concentric iron rings on which the pots were placed. Depending on the size of the pot or the heat needed, one could remove the inner rings.
Modern stove designs
Corn and pellet stoves and furnaces are a type of biofuel stove. The shelled dry kernel of corn, also called a corn pellet, creates as much heat as a wood pellet but generates more ash. "Corn pellet stoves and wood pellet stoves look the same from the outside. Since they are highly efficient, they don't need a chimney; instead they can be vented outdoors by a four-inch (102 mm) pipe through an outside wall and so can be located in any room in the home."
A pellet stove uses small, biological fuel pellets which are renewable and very clean-burning. Home heating using a pellet stove is an alternative currently used throughout the world, with rapid growth in Europe. The pellets are made of renewable material –- typically wood sawdust or off-cuts. There are currently more than half a million homes in North America using pellet stoves for heat, and probably a similar number in Europe. The pellet stove typically uses a feed screw to transfer pellets from a storage hopper to a combustion chamber. Air is provided for the combustion by an electric blower. The ignition is automatic, using a stream of air heated by an electrical element. The rotation speed of the feeder and the fan speeds can be varied to modulate the heat output.
Other efficient stoves are based on Top Lit updraft (T-LUD) or Woodgas or Smoke Burner stove a principle applied and made popular by Dr. Thomas Reed, which use small pieces of sticks, chips of wood or shavings, leaves, etc as fuel. The efficiency is very high up to 50 percent as compared to traditional stoves which are 5 to 15 percent on an average.
Emissions
Many countries legislate to control emissions. In the United States, the Environmental Protection Agency created stricter emissions standards in the late 1980s. Maximum smoke output is limited to 7.5 grams per hour.
The burn temperature in modern stoves can increase to the point where secondary and complete combustion of the fuel takes place. A properly fired masonry heater has little or no particulate pollution in the exhaust and does not contribute to the buildup of creosote in the heater flues or the chimney. Some stoves achieve as little as 1 to 4 grams per hour. This is roughly 90% less smoke than older stoves, and equates to nearly zero visible smoke from the chimney. This is largely achieved through causing the maximum amount of material to combust, which results in a net efficiency of 60 to 70% as contrasted to less than 30% for an open fireplace. (Net efficiency is the amount of heat energy transferred to the room compared to the amount contained in the wood, minus any amount central heating must work to compensate for airflow problems.)
Origin
The Old English word stofa meant any individual enclosed space, such as a room, and 'stove' is still occasionally used in that sense, as in 'stoved in'. Until well into the 19th century 'stove' was used to mean a single heated room, so that Joseph Banks assertion that he 'placed his most precious plants in the stove' or René Descartes observation that he got 'his greatest philosophical inspiration while sitting inside a stove' are not as odd as they seem.
In its earliest attestation, cooking was done by roasting meat and tubers in an open fire. This form of cooking is still the mainstay of groups such as the Hadza. Pottery and other cooking vessels may be placed directly on such a fire, but setting the vessel on a support resulted in a stove, the simplest of which is a base of three stones. The three-stone stove is still widely used around the world. In some areas it developed into a U-shaped dried mud enclosure with the opening in the front for fuel and air, sometimes with a second smaller hole at the rear.
Kitchen stove
A kitchen stove, cooker or cookstove is a kitchen appliance designed for the purpose of cooking food. Kitchen stoves rely on the application of direct heat for the cooking process and may also contain an oven underneath it which is used for baking.
See also
External links
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