Using wood for heating
According to government figures (from BERR), heating buildings and water uses about one third of all energy (including transport) in the UK. Much of this energy is supplied by fossil fuels, and so is resulting in large amounts of carbon dioxide being emitted, contributing to climate change.
Wood has been used to provide heating for thousands of years, but with the convenience of gas, electricity and heating oil in the UK there is now a significant quantity of wood that could be used for sustainable heating but is not. Some of this comes from waste, such as tree surgery arisings and the building industry, but there is significant scope for managing woodland to produce wood for heating. Burning wood is carbon-neutral, as the carbon dioxide emitted when it burns was absorbed from the air while the tree was growing. If this replaces the use of a fossil fuel then it has helped tackle climate change.
Woodland management for wood fuel
As a woodland owner the use of wood for heating is worth thinking about. Management of woodland, done properly, can be helpful to wildlife and biodiversity, and also make the wood a more pleasant and interesting place to be. Coppicing in particular is very sustainable, as after harvesting the wood the tree is still alive and will grow back extremely rapidly, as we found in our own wood, where the sweet chestnut re-grew to a height of six feet during the summer after cutting. Coppicing also makes a unique habitat that some species of birds and insects depend on, and it encourages a wide diversity of ground-level flora. Having said this though, whatever management technique is used, it is important to leave plenty of dead wood lying around, as many fungi and insects need it to feed on, and other creatures in turn feed on them.
Many woodland owners will produce wood fuel on a small scale, processing it by hand. In order to get the best out of the wood, you should:
- Fell trees in the winter, when there is less sap in the wood.
- Split the wood as soon as possible to allow it to start drying.
- Store the split wood with plenty of space for air to flow round it, and with some shelter overhead to keep the rain off (but not at the sides, so air can get in).
- Store the split wood for as long as possible before burning it. Aim for a minimum of two months of warm weather, but longer if possible.
Seasoning the wood (allowing it to dry out) is important, as you will get about 20% more heat out of a piece of wood when it has been seasoned compared to when it was green. If you can season it in your woodland, then it will be easier to carry out afterwards as it will be lighter. One tip we learned recently was to split the wood in long lengths (a couple of metres) using wedges, and stack it to dry in such a way that when you're ready to use it you can slice through the whole stack repeatedly with a chainsaw, cutting the ready-split wood to the length you need.
Using the wood fuel
You will obviously get the most out of the wood fuel you produce if you can use it yourself. While an open fire is pleasant to look at, the efficiency can be as low as 10%, because so much air is drawn into the house, heated, and then sent up the chimney. In addition to this there can be incomplete combustion of the wood, causing the emission of some gases that contribute to climate change, and others that are local air pollutants.
A stove can do much better, being perhaps 40-70% efficient and achieving near-complete combustion, depending on the design and how it is used. It is important to choose the right capacity of stove for the space you want to heat. If it is too small then it will need to be run very hot, and will send excess heat up the chimney and reduce the efficiency, while if it is too large it will be run at a low power, causing pollution and reduced efficiency due to incomplete combustion. You should take advice from a stove installer on what would suit your house best.
Aside from open fires and stoves, there are also boilers that will burn wood pellets or wood chip. Pellet boilers (or stoves) are available in small capacities, but you're unlikely to be making wood pellets yourself so you will be dependent on a supplier, and the pellets could be travelling a long distance to reach you. Boilers burning wood chip are only available in larger sizes, suited to public or commercial buildings. Although you're unlikely to install your own wood chip boiler, you could help supply one, as explained below.
Supplying wood fuel
If you find you have more wood fuel than you can use yourself, you might decide to start supplying it to other people. The simplest way to do this is in the form of split logs for an open fire or stove, but producing wood chip is another option. Chipping machines come in various sizes, but even the smallest will process tens of tonnes of wood in a day, so you would expect to hire one (with an operator) rather than buy one. Also, you may well need to team up with your woodland neighbours to provide a big enough pile of logs to keep the chipper busy for a day. Finally, you will need a customer for the wood chip, but fortunately there are several groups across the country setting up schemes to pool the wood resources in a region and sell them to large customers. The details of some of these groups are given below.
Ashden Awards wood fuel winners
In my work for the Ashden Awards for Sustainable Energy I've come into contact with a range of people working with wood fuel. Over the past few years we've given a range of awards in the UK to organisations using wood fuel for heating. The links below take you to information on them, including detailed case studies and short documentary films:
Thames Valley Bioenergy won an award for their work collecting wood fuel from woodland management, tree surgery and short rotation coppice and supplying it to customers such as a power station and local schools.
BioRegional Development Group won an award for creating a "TreeStation" in Croydon, which allowed local tree surgeons to drop off their waste wood instead of sending it to landfill. The wood is chipped, dried and then delivered to customers in the region.
Wood Energy won an award for their work installing wood chip boilers across the UK, and helping set up local wood fuel supply chains.
Barnsley Metropolitan Borough Council won an award for their work in collecting tree surgery waste from their own parks and gardens and using it to run boilers in council flats and offices.
Nottinghamshire County Council won an award for their project to convert schools with coal-fired boilers to run on wood pellets instead.
The Rural Energy Trust promotes the use of wood fuel in schools and public buildings, giving training, demonstrations and presentations to encourage the sustainable production and use of wood fuel.