There are two main types of wood fuels used with automated feed boilers:
- wood pellet boilers - these use a processed wood fuel, currently usually imported (although UK suppliers are coming on line gradually). It is a more expensive fuel, but requires a cheaper type of wood boiler. Fully automated (you need a big storage area for the pellets, but they can be blown in from a tanker, so the tanker can be up to 30m away from the fuel store)
- wood chip boilers - these use a 30% moisture content wood, chipped from the unused wood after logging in managed forests in the UK. Because it is less processed, it is cheaper compared to the pellets, but the boiler required is more substantial. Again, it is fully automated input, and automatic ash removal. The cost of the wood chip boiler is greater than a wood pellet boiler (although a wood chip boiler can be used for wood pellets too.
Wood fuel boilers are really best used in situations where a church building is used a lot during the week as well. They don't work so well if they have to start up from scratch weekly, but work better if they can simply 'slumber' between daily firings. However, you'd need to talk to the particular manufacturers about that.
What a supplier would need to know is what you are currently using in quantities of fuel - over the last 2 or 3 years. From this, they can calculate the number of kWh that you are likely to need, and therefore the supplier can tell you what size of a boiler you would require. Wood fuelled boilers are much bigger than oil or gas boilers, and you need significant space to accommodate the fuel. Particularly for wood chip, there would need to be access for a tipping lorry, and preferably a below ground store for the wood chip, next door to where the boiler is. The store needs to be significant in size so that you don't have to have the lorry delivering small amounts often.
The automated ash removal system puts the ash into a box or bin which needs then to be removed every 2 - 4 weeks.
The main questions you need to ask before contemplating a wood fuelled boiler are:
- do you have space for a large fuel hopper?
- do you have space for a large boiler next door to the hopper (or a space that could be separated easily - the wood fuel store needs to be physically separated but next to the boiler for safety reasons)
- do you have access for lorries to deliver into the fuel hopper? (This may not be so relevant if you go down the wood pellet road.)
- does your building get a lot of use during the week, which would work better for wood fuelled systems?
- are you prepared to put in a large amount of money up front for installation of a system which will save you money in the long run, and reduce your dependence on fossil fuels?
The National Energy Foundation's wood fuel site is regularly updated with suppliers' details, but the funding for the project came to an end, so other information on the site is not updated. However, it is still a useful source of information about wood fuelled boilers.