Efficiency
Compared to simple open fires, enclosed stoves can offer greater efficiency and control. In free air, solid fuels burn at a temperature of only about 240 °C (464 °F), which is 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 (600 °C/1,112 °F) 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 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.
An early improvement was the fire chamber: the fire was enclosed on three sides by masonry 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 in an attempt to improve efficiency.
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.
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Famous quotes containing the word efficiency:
““Never hug and kiss your children! Mother love may make your children’s infancy unhappy and prevent them from pursuing a career or getting married!” That’s total hogwash, of course. But it shows on extreme example of what state-of-the-art “scientific” parenting was supposed to be in early twentieth-century America. After all, that was the heyday of efficiency experts, time-and-motion studies, and the like.”
—Lawrence Kutner (20th century)
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—Baruch (Benedict)
“I’ll take fifty percent efficiency to get one hundred percent loyalty.”
—Samuel Goldwyn (1882–1974)