Heat From Wood

Wood has been burned as a source of heat ever since the ancestors of modern humans first learned how to control fire about 1.5 million years ago. Today, as we look for environmentally sustainable ways to produce heat, wood has taken on a new significance because it is renewable, and (depending on how it is processed & where it comes from) can be virtually carbon neutral: the CO₂released by burning wood is equal to the amount trapped by the tree as it grew. It is also the cheapest form of renewable energy to install, with prices from about £300 for a small domestic wood burning stove to about £3500 for a much larger boiler system.

Fire technology

Open fires are a traditional feature of houses in the UK, but for domestic heating the most efficient way to generate heat from wood is by using a well maintained wood burning stove. Open fires are the least energy efficient way of using wood for heating; they typically operate at 15-20% efficiency - meaning that only 15-20% of the heat generated goes back into the room while 80-85% is lost up the chimney. By comparison a wood burning stove works at around 75% efficiency so one log in the wood burner produces as much heat as 4 logs on the open fire. An alternative to a log burning stove is a pellet stove. These use pellets for fuel, typically made of compressed sawdust or other types of plant biomass. Pellet stoves cost more to buy than a wood burning stove, but require much less maintenance and can be set to run automatically. The price of pellets is competitive with logs as a fuel source, and both pellets and logs are considerably less expensive than coal or oil, and can be practically carbon neutral. Many wood burners and pellet stoves are fitted with a back boiler which can be used for hot water or plumbed into the radiators or underfloor heating system.

Choosing your fuel

The efficiency of wood as a fuel depends a great deal on what sort of wood it is and how dry it is. Hardwoods (deciduous trees, such as oak and beech) and softwoods (pines and firs) can both be used for fuel, but because the density of softwoods is about half that of hardwoods one would need about twice the volume of softwood to produce the same amount of heat.

To maximise fuel efficiency, any firewood should ideally have been stored somewhere dry for at least a year before burning, to dry the wood out. Green wood has a much lower heating capacity than dry wood as some of the heat is used to drive off the moisture in the wood. Beech, oak and ash are all excellent as wood fuel if they have been properly dried.

When selecting and preparing logs for burning the ideal size of log for most efficient combustion is less than 10 centimeters thick - bigger logs should be split down to this size.

Grants

Grants towards the cost of biomass heating systems are available through the Low Carbon Buildings programme. Visit their website or phone in for details of eligibility and how to apply.

www.lowcarbonbuildings.org.uk

0800 915 7722

Useful Contacts:

Please note that this list of suppliers is not exhaustive. The companies listed are offered as a starting point for your enquiries but with no implied recommendation as to their qualities of service to the public.

Country Cookers

01432 342351

Euroheat Distributors Ltd

01885 490474 www.euroheat.co.uk

Clearview Stoves

01588 650401 www.clearviewstoves.com

Continental Fires Ltd

01694 724199 www.confires.demon.co.uk

The Organic Energy Company

0845 458 4076 www.organicenergy.co.uk

Further Information:

Marches Wood Energy Network