Cooking Stove

A stove is an appliance that may be used for heating, cooking, or both. Stoves differ from open fires in that they are easier to control, are more efficient, and may create less pollution.

An open fire does not burn efficiently or remove the smoke. Modern stoves burn efficiently and pollute less because they vaporize the fuel thoroughly, mix it with an optimized amount of air, and burn it at optimal temperatures. When heat is extracted, modern stoves often include contraflow heat exchangers so efficient that they condense water from the exhaust.

To maintain efficiencies, modern stoves must be kept clean, including the exhaust flue.

The result of these high efficiencies is that the stove uses less fuel and emits less pollution while producing the desired amount of heat.

Alsatian stove in Fouday church

 

Efficiency

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. 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 order to prevent air—and therefore smoke—from spilling back into the room, there must be a large updraft to pull air (and therefore heat) out of the chimney. The updraft  pulls heat away as well as pulling air from the rest of the house into the fire and then up the chimney. A fireplace consumes 200 to 600 ft³ (17 m³) of air per minute, more for a very large fire. Even a mostly closed-off fireplace, for example a modern fireplace with glass doors closed, will use 50–150 ft³ 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 and thus does not ignite and is lost. By controlling the inflow of air to allow only what a fire needs to burn, modern stoves can reduce the consumption of air to as little as 15–30 ft³ per minute, though consumption varies.

Modern stoves also increase the completeness of combustion by capturing 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. More expensive 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 and to preheat the air prior to its entering the combustion chamber. Modern enclosed stoves are often built with a window to let out some light and to enable the user to view the progress of the fire. Glass and semitranslucent manufactured mica are common materials used for these windows.

Material

Tile stove (for heating) in the dining room of the Catherine Palace, St. Petersburg

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 for 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 be another 30 years before the technology would be refined and the size of the iron stove would be reduced enough for domestic use. Philo Stewart’s Oberlin stove was a much more compact, wood-burning cast-iron stove, patented in the US 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 specialized 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

A high-end stove called the AGA cooker was invented in 1922 by Swedish Nobel prize winner Gustaf Dalén. 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.

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. From the outside, corn pellet stoves and wood pellet stoves look very similar. Both types are highly efficient. These stoves do not need chimneys;  they can be vented outdoors using a pipe that goes through an outside wall.

A pellet stove uses small, biological fuel pellets that 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 for the combustion is provided by an electric blower. The ignition is automatic, using a stream of air heated by an electrical element. The fan speeds and the rotation speed of the feeder can be varied to modulate the heat output.

Emissions

In the US, 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 figure represents roughly 90% less smoke than that generated by older stoves, an amount which equates to nearly zero visible smoke from the chimney. The reduction in smoke is largely achieved through causing the most possible material to combust, resulting in a net efficiency of 60 to 70% as contrasted with 0 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 airflow problems.)

Kitchen Stove

An image of a modern 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, used for baking.

As stoves replaced open fires and braziers as a source of more efficient and reliable heating, models were developed that could also be used for cooking. These models came to be known as kitchen stoves. When homes began to be heated with central heating systems, there was less need for an appliance that served as both heat source and cooker, so stand-alone cookers replaced the kitchen stoves.