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How Wood Burning Stoves Work

Posted on 13 December 2016

 

If a wood burner is being used to replace an older style open fire, it has the potential to reduce your house's carbon footprint by at least 14%. An open fire will only provide you with 30% efficiency, as the majority of heat is lost through the chimney. Whereas, a wood burner will give you around 76-89% efficiency.

 In most cases, some or all of the following features will be included in a stove: an 'Airwash system' for the window, a 'Cleanburn system' with secondary air, an 'External air facility' and an integral boiler to provide domestic hot water and run radiators.

  As a guide, it is suggested that for every 14 cubic meters of space, you will need 1kw (approx), of heat output. This will achieve a room temperature of 21 degrees. This however, is a rough guide and does not take into account a number of other important factors such as the age of your home, how well insulated it is, how many rooms are to be heated, and whether or not your living space is open plan.

Key points to consider before selecting the right stove

1) Style/ aesthetics you desire

2) Required heat output appropriate for the room size

3) Fuel type - wood burning only or multi-fuel

4) Do you wish the stove to heat water as well as the room

5) Are cleanburn, airwash and efficiency important to you

6) Do you wish to burn wood in a 'smoke control area'

Wood burns best on a bed of ash,  with its combustion air coming from above. Therefor, wood burning stoves have a flat fuel bed and no ashpan.

Multi-fuel stoves usually have a riddling grate for the effective combustion of solid mineral fuels but, also have Airwash so they can effectively burn wood aswell.

Primary Air

This is the air that is drawn into the wood burning stove, typically at a low level to maintain the combustion of the solid fuel being burnt. The control to adjust this air is usually found on the front of the stove, this regulates the amount of air entering the firebox. This gives you the opportunity to determine the intensity of the fire, so the customer has control. This, in turn will alter the heat output.

Airwash System

A specific design feature which,  uses a specifically placed vent or vents to draw in cool air from the room; the air is then heated and ducted to 'wash' over the inside of the glass. This feature helps to keep the glass clean for longer, allowing you to enjoy the natural glow,  and flames to the full.

Convection Air

Cool air is drawn in from the room,  and is carried into the convection chamber. It is then heated as it rises within the stove,  before flowing out into the room. The hot air rising draws more cool air into the stove, setting up a continuous flow and maintaining added heat efficiency.

Cleanburn System

Wood burning stoves incorporate triple air systems to provide a cleaner burn, greater thermal efficiency and control of the flame.

Airwash air is drawn down over the inside of the window, to keep the glass clean and clear. It is also used as primary combustion air when burning wood.

Primary air for use with solid fuels, also used to start wood fires but, not normally used once a wood fire is burning.

Cleanburn secondary air is pre-heated as it passes through a heat exchanger chamber within the firebox. It is then drawn into the smoke stream, where it combusts unburnt hydrocarbons to provide a cleaner burn and greater thermal efficiency.

Introducing pre-heated secondary air into the firebox at just the right point promotes efficient combustion of any unburnt hydrocarbons found in the smoke. This 'Cleanburn' process can greatly increase the combustion efficiency of your wood burning stove, and dramatically reduce the amount of unburnt particles going up the chimney. This in turn can reduce your servicing costs and save you money in fuel. It also gives you an improved flame visual.

External Air

All Wood burning stoves with a heat output above 5KW require an additional flow of air, and provide Oxygen into the room. Thus encouraging the combustion process. An external air facility allows this air to come directly from outside your building, rather than through a vent into the room, thus eliminating draughts and adding to the overall heating efficiency.

Boiler stoves

These are specifically designed to provide domestic hot water and/ or run radiators as part of a stand alone system. Alternatively you can 'link up' some boiler stoves with your existing heating system.  The 'link up' system can connect with gas or oil sealed heating systems, combi boilers, underfloor heating, advanced electronic controls and solar panels. This will help save money on fossil fuels and reduce your reliance on single-source heating.

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