When considering the installation of a wood fuelled stove the following design issues should be addressed.

• Planning Issues

The following planning and regulatory issues must be considered:

1. Regulations - The installation must comply with all safety and building regulations (see Part J of the Building Regulations).
2. Smokeless zone - Wood can only be burnt on exempted appliances, under the Clean Air Act. This mainly applies to domestic appliances.
3. Planning - If the building is listed, or in an area of outstanding natural beauty (AONB), then you will need to check with your Local Authority Planning Department before a flue is fitted.

An accredited installer will be able to provide more detailed advice regarding suitability.

• Design Issues

One of the most important design aspects of any wood fuelled stove is the design and installation of the flue or chimney. The vent material must be specifically designed for wood fuel appliances and there must be sufficient air movement for proper operation of the stove. Existing chimneys can be fitted with a lined flue to protect against tar build up. In addition, it is essential to insulate chimneys in order to maintain the temperature of the flue gases. Whenever steam is in the chimney the temperature at its outlet must be above 100ºC to avoid water condensing. Visible smoke emission from the chimney is a sign of inefficient burning.

• Feedstock storage/supply issues

It is important that there is sufficient storage space for the fuel as well as appropriate access to the boiler for loading and a local fuel supplier.

A basic wood fuelled stove will require around 5 tonnes of wood per year, assuming that it is in use most of the time from October to April. Unseasoned wood is heavier because of the water content and therefore the wood must be stored, under cover, to reduce its moisture content prior to burning. Trees are best felled in the winter when moisture content is lower, then cut and split to dry better. Storing them under cover for at least one summer should then reduce the moisture content to around 25%.

Ash is probably the best firewood, as it has the lowest moisture content when green (c. 35%), but beech, cherry and hawthorn are also good. Second-hand construction timber should not be used as it is probably treated and will release toxic fumes. Chipboard, plywood or mdf should not be used – even for kindling – as it contains formaldehyde. However, in general, wood ash, containing potash, can be used as a fertilizer (best applied at the end of the growing season, and not on alkaline soil).

Wood pellets are available from many sources and their distribution is increasing as systems become more popular. Wood pellets are uniform in size and flow easily so can be transported automatically from large silos to the boiler as required. There are various automatic feeding systems available including worm feed, suction probe, rotating worm screw, silo bag and underground pellet tank.

As wood pellets are compressed, they take up less room than other forms of wood fuel. Their uniform shape allows them to flow making the automation of fuel handling easy and typically the cost of the boiler less than wood chip and log burning systems.

• Site Assessment 

When assessing a potential site for a retrofit installation it should be noted that old chimneys will need re-lining, as tar could be deposited, causing a fire hazard, plus gases could seep through into living areas. Chimneys must be swept every year to remove creosote and tar and avoid chimney fires.