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Wood-burning stove: Wikis

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For a list of stove types see Stove (disambiguation).

A nineteenth century example

A wood-burning stove is a heating appliance capable of burning wood fuel and wood-derived biomass fuel. Generally the appliance consists of a solid metal (usually cast iron or steel) closed fire chamber, a grate and an adjustable air control. The appliance will be connected to a suitable chimney or flue which will fill with hot combustion gases once the fuel is ignited. It is critical that the chimney or flue gases be hotter than the outside temperature as this will result in combustion gases being drawn out of the fire chamber and up the chimney.

Contents

Important information on burning wood

Wood-burning stove heating a grocery, Detroit, 1922.
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Hardwood or softwood

Clearly there are different types of wood, but they will usually fall into either the hardwood or softwood types. Both types of wood have the same energy content (by mass) and will provide similar energy outputs. However, the essential difference will be in the rate at which the fuel burns. Hardwoods derived from slow-growing broadleaf trees will burn at a slower rate for sustained output. Softwoods are derived from evergreen trees such as conifers, which are fast growing but burn at a far greater rate.

Moisture content

One of the most critical factors in wood burning is the moisture content of the wood, as any water in firewood has to be boiled off during the burning process. But the moisture content can be reduced by seasoning. Freshly cut wood will contain a moisture content of around 65-90%. This wood should never be used for firewood. Apart from producing very low heat outputs this wet wood will also generate large amounts of soot and tar, which can potentially lead to chimney fires (as these particles will coat the chimney and will fuel a chimney fire).

For best results firewood should have a moisture content of less than 20%. The process of removing the excess moisture is called seasoning. Seasoning by air drying the wood can take up to two years. Wood should be stored in a well ventilated (but covered) structure, outdoors. A recent innovation is kiln dried wood. With interest and usage of wood burners at an all time high, some companies are now using large kilns to quickly dry their wood. Hardwood should be seasoned for longer with some taking up to four years to season. Hardwood is seasoned by being left out to the elements for 3-4 winters then a summer under cover with ventillation to dry out.

Softwood is left out for two winters to the elements then one summer to dry out with ventilation

Air supply

A damper in a stove chimney flue (1) controls air supply by being set open (2) or closed (3).

High heating efficiencies on closed appliances can only be attained by controlling the supply of air to the fire chamber (operating the air control correctly). It is not recommended to leave the air control fully open, beyond the point of getting the chimney/flue hot initially. A fully open air control will lead to more heat being sent straight up the chimney rather than into the room (reduced efficiency). The biggest problem with leaving the air control fully open is “overfiring”. Overfiring is caused when too much heat is generated within the fire chamber, which will lead to warping, buckling and general damage to the stove and its internal components. Individual stoves will have their own quirks, so take a little time to get used to a new stove's settings.[1]

Safety

Correct air flow and ventilation is also critical to efficient and safe wood burning. Specific requirements will be laid down by the stove manufacturer. Legal requirements for new installations in the UK can be found in Building Regulations Approved Document J, Section 2, Table 2.1 "Air Supply to a solid fuel appliance" [2].HETAS heating engineers act as a one stop shop. They fit and certify the stove, more expensive than using the council,but it takes away any hassle or worry [1]

Smoke Control Areas

Under the United Kingdom's Clean Air Act local authorities may declare the whole or part of the district of the authority to be a smoke control area. It is an offence to emit smoke from a chimney of a building, from a furnace or from any fixed boiler if located in a designated smoke control area. It is also an offence to acquire an “unauthorised fuel” for use within a smoke control area unless it is used in an “exempt” appliance (“exempted” from the controls which generally apply in the smoke control area). The current maximum level of fine is £1,000 for each offence.

In order to comply with the Clean Air Act in "smoke control areas", an exempt appliance or fuel must be used. [3].

Types

  • Benjamin Franklin invented the Franklin stove, a more efficient type of wood-burning stove.
  • Carl Johan Cronstedt is reported to have increased efficiency of wood-burning stoves by a factor of eight in the mid-18th century.
  • Inserts It is possible to convert wood burning fireplace to a wood burning stove with a fireplace insert. A fireplace insert is a self-contained unit that sits inside the existing fireplace and chimney. They produce less smoke and require less wood than traditional fireplaces. Fireplace inserts come in different sizes for large or small homes.[4]

See also

References

  • HETAS List No.14 2007 "The official guide to approved solid fuel products and services"

External links


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