cooktops

There are many types of stoves. A kitchen stove is used to cook food, and refers to a device that has both burners on the top (also known as the cooktop or range or, in British English, the hob) and, often, an oven. A cooktop just has burners on the top and is usually installed into a countertop. A drop-in range has both burners on the top and an oven and hangs from a cutout in the countertop (that is, it cannot be installed free-standing on its own).

In industrial usage, stove may refer to the place where fuel is combusted before being fed to a large heat consumer such as an open hearth furnace.

Kitchen stove heat generation

A stove generates heat by one or more of the following means:

• burning of
  • natural gas
  • liquefied gases (e.g., butane, propane)
  • heating oil
  • biofuel such as wood, coal, corn, or synthetic heating pellets
• electrically, by either
  • electrical resistance (by way of a heating element)
  • induction

Modern stove features

Modern stoves are typically considered a basic appliance in homes in developed nations. Along with the refrigerator, a stove is usually found in the kitchen.

Many modern stoves typically have from two to eight burners or plates of various sizes and power levels; an oven; and knobs, for controlling the heat of the burners and the oven. The control knobs may be located on the backsplash, on the cooktop, or on the upper part of the front of the stove.

Middle- to high-end models also may feature locking mechanisms for the oven door; convection cooking; automatic cleaning mechanisms, which raise the oven temperature to more than 260 degrees Celsius (500 degrees Fahrenheit) and reduce accumulated food spills to ash or a catalytic oven lining which aids in burning off spills; one or more timers; and a digital display. Many can even accommodate automatically raising and lowering the oven temperature to preset levels at preset times.

History

Early stoves in the Western World

In Europe, the history of the kitchen stove begins in earnest in the 18th century. Before that time, people cooked over open fires fuelled by wood, which first were on the floor or on low masonry constructions. In the Middle Ages, waist-high brick-and-mortar hearths and the first chimneys appeared, so that cooks no longer had to kneel or sit to tend to foods on the fire. The fire was built on top of the construction; the space underneath was used to store and dry wood. Cooking was done mainly in cauldrons hung above the fire or placed on trivets. The heat was regulated by placing the cauldron higher or lower above the fire.

Open fire has three major disadvantages that prompted inventors even in the 16th century to devise improvements: it is dangerous, it produces much smoke, and the heat efficiency is poor. Attempts were made to enclose the fire to make better use of the heat that it generated and thus reduce the wood consumption. A first step was the fire chamber: the fire was enclosed on three sides by brick-and-mortar walls and covered by an iron plate. This technique also caused a change in the kitchenware used for cooking, for it required flat-bottomed pots instead of cauldrons. 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.

Early stoves in Asia

Chinese and Japanese civilisations had discovered the principle of the closed stove much earlier. Already from the Chinese Qin Dynasty (221 BC - 206/207 BC), clay stoves that enclosed the fire completely are known, and a similar design known as kamado (かまど) appeared in the Kofun period (3rd - 6th century) in Japan. These stoves were fired by wood or charcoal through a hole in the front. In both designs, pots were placed over or hung into holes at the top of the knee-high construction. Raised kamados were developed in Japan during the Edo period (1603 - 1867).

Wood stoves (metal stoves, masonry stoves)

Although a good source of light before lamps, an open fireplace is a very inefficient form of heat for two reasons. First, in order to prevent air, and therefore smoke, from spilling back into the room you need a large updraft pulling air (and therefore heat) out the chimney. This both pulls heat away and pulls air from the rest of the house into the fire and then up the chimney. A fireplace consumes 200 to 600 cubic feet of air per minute, more for a very large fire. A mostly closed off fireplace, for example a modern fireplace with glass doors closed will use 50-150 cubic feet per minute. High airflow creates a draft which pulls heated air out of the house to be replaced with cold air leaking in from the outside. Second, in an open fire some of the combustible gas coming off the wood escapes does not ignite and is lost. To resolve these problems masonry heaters were developed, then metal stoves came into use in the 18th century.

An early, and famous, example of a metal stove is the Franklin stove, a wood burning 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 stove 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. Stewart's Oberlin stove was a much more compact metal 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 veritable cooking machines 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.

By controlling the inflow of air to allow only what a fire needs to burn, metal stoves reduce the consumption of air to a mere 15-30 cubic feet per minute (this figure is for a modern stoves. All metal stoves operate on the principle of controlled air flow but their consumption will vary).

Modern wood stoves also increase the completeness of combustion. More expensive stoves use a catalytic converter which causes the gas and smoke particles not actually burned to combust. Other models use a design that includes firebox insulation, a large baffle to produce a longer, hotter gas flow path and pre-heating the air prior to its entering the combustion chamber.

A masonry heater is designed to allow complete combustion by burning fuels at full-temperature with no restriction of air inflow. Because the firebox is masonry (not metal) the burn temperature can increase to the point where secondary and complete combustion of the fuel takes place. These heaters capture most of the heat from the combustion and exhaust through an extended system of flues inside a large thermal mass before the exhaust is vented to the outside air. 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. 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.

In the US, the EPA created stricter emissions standards in the late 1980s. Maximum smoke output is limited to 7.5 grams per hour and some stoves achieve as little as 1 to 4 grams per hour. Put differently, this is roughly 90% less smoke than older stoves, which equates to nearly zero visible smoke from the chimney. This is largely achieved through causing the most possible material to combust, which results in a net efficiency of 60 to 70% as contrasted to zero to 30% for a 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 the airflow problems described elsewhere in this article.)

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. Glass or semi-translucent manufactured mica are common window materials.

Gas and electric stoves

All previous stoves were fueled by wood (or other biofuel), charcoal, or coal. The first gas stoves were developed already in the 1820s, but these remained isolated experiments. (James Sharp in Northampton, England, patented a gas stove in 1826 and opened a gas stove factory in 1836.) At the World Fair in London in 1851, a gas stove was shown, but only in the 1880s did this technology start to become a commercial success. The main factor for this delay was the slow growth of the gas pipe network. The first gas stoves were rather unwieldy, but soon the oven was integrated into the base and the size reduced to fit in better with the rest of the kitchen furniture. In the 1910s, producers started to enamel their gas stoves for easier cleaning. A high-end gas stove called the AGA cooker was invented in 1922 by Swedish Nobel prize winner Gustaf Dalén. It is considered to be the most efficient design and is a much sought after kitchen "must have" in certain circles—despite the hefty price tag.

The AGA, and similar products such as the Rayburn Range are examples of always-on stoves which continue to burn fuel even when cooking is not being performed. Stoves (or ranges as they are also known) such as these are often used instead of boilers or furnaces to supply hot water and central heating to the rest of the house.

Thomas Ahearn invented the electric cooking range in 1892 and installed one in the Windsor Hotel in Montreal. The electric stove was showcased at the Chicago World's Fair in 1893, where an electrified model kitchen was shown. But like the gas stove, the electrical stove had a slow start, partly due to the unstable technology, and partly because first cities and town needed to be electrified. By the 1930s, the technology had matured and the electrical stove started to slowly replace the gas stove, especially in domestic kitchens.

The electrical stove technology has developed in several successive generations:

• The first technology used resistor heating coils which heated iron hotplates, on top of which the pots were placed. Though the technology is slowly fading into obsolecence, coil ranges still provide the best durability out of all electric cooktop implementations.
• In the 1970s, glass-ceramic cooktops started to appear. Glass-ceramic has a very low heat conduction coefficient, but lets infrared radiation pass very well. Electrical heating coils or infrared halogen lamps are used as heating elements. Because of its physical characteristics, the cooktop heats quicker, there is less afterheat, and only the plate heats up while the adjacent surface remains cool. Also, these cooktops have a smooth surface and are thus easier to clean, but they only work with flat-bottomed cookware and are markedly more expensive.
• A third technology, developed first for professional kitchens, but today also entering the domestic market are induction stoves. These heat the cookware directly through electromagnetic induction and thus require pots and pans with ferromagnetic bottoms. Induction stoves also often have a glass-ceramic surface.

The iron hotplate technology is still in widespread use, although newly equipped kitchens nowadays usually get a stove using one of the later technologies.

Electrical oven technology has also advanced: in the convection oven, a stream of hot air is used for heating food instead of the heat produced by coils directly as in a conventional electrical oven.

Gas and electric stoves are the most common today in western countries. Both are equally mature and safe, and the choice between the two is largely a matter of personal preference and preexisting utility outlets: if a house has no gas supply, adding one just to be able to run a gas stove is an expensive endeavour. In particular, professional chefs often prefer gas cooktops, for they allow them to control the heat more finely and more quickly. On the other hand, chefs often prefer electric ovens because they tend to heat food more evenly. Today's major brands offer both gas and electric stoves, and many also offer dual-fuel stoves combining gas cooktops and electric ovens.

Modern corn, pellet or biofuel stove

Main article: Corn and pellet stoves and furnaces

A corn stove is a type of pellet stove which is 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 pipe through an outside wall and so can be located in any room in the home." Encyclopedia of Alternative Energy

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.

See also

• Beverage-can stove
• Furnace
• Kitchen
• Oven
• Portable stove
• Franklin stove
• Rocket stove
• Smokeless and wood conserving stoves

References

• Woodheat.org information on woodstoves
• Woodheat.org information on open fires

External links

• History of iron stoves – in German.
• The History of Stoves and Ovens From About.com
• How Stoves Work Article by RepairClinic.com
• Early Chinese stoves, with images.
• Early Japanese stoves, with a good image.
• The First Pellet Stoves, the first recorded pellet stove.
• Masonry Heater Association