If you are considering “biomass” as a heating system the most obvious choices are between log burning boilers and wood pellet boilers.
For some the clear advantages of log boilers are:
- Cost of installation
- Cost of fuel
- Sustainable use of wood
For others the clear advantages of pellets are:
- Automation of heating
- Higher efficiency
- Pellets are a waste product
- Space saving
Cost of Boiler
Log boilers such as the WBS active are MCS accredited and burn wood up to 90% efficiency. The boilers start at at a little over £1000 (20kW WBS) and this is a lot cheaper than the Pelleburn wood pellet boiler that starts at £3500.
Cost of Extra Water Heating
Wood pellet boilers modulate. This means that they can adjust to produce the amount of hot water that you need to store for heating. Log boilers need to heat water when they are burning otherwise there is nowhere for the heat to go. This is often in the range of 30-50l per kW.
For instance a 20kW log boiler will need to heat 600-1000l of hot water.
You could choose an accumulation tank or a thermal store to do this.
An accumulation tank or “buffer store” can used to store the heat. They are well insulated and once heated can distribute the heat without the need for the boiler to be “on”. A 1000l buffer store is nearly 1 meter diameter by 2 meters tall. This does mean that you need to find space for this. The buffer store will be an extra £1000+ and there are extra plumbing costs in installation.
A thermal store can incorporate a hot water tank and heating hot water in one tank. A “tank in tank”. Assuming you need hot water for baths and showers, then you will need a hot water tank. Some houses already have these, some do not. Others are old and need replacing. A thermal store is a good solution if there is a need for a new hot water tank.
Wood pellet boilers do also benefit from the use of accumulation however they can burn efficiently for shorter periods of time and so need less water to heat. On smaller systems it is possible to work without one, however your boiler may need to come on more often. Using an accumulation tank may prolong the life of your parts.
In summary – log boilers need more accumulation than pellet boilers, and this will increase costs of installation. This will vary depending on the installation.
Wood pellet boilers that are completely automated generally infers a large pellet store that can be filled. This can take up a lot of space e.g. 10m3. This has to be dry and purpose built. Whilst there are pellet stores that can be outside for most homes the choice is between a top loading boiler (ie no storage) e.g. an MCZ Musa , an indoor pellet hopper e.g. Pelleburn or a purpose built hopper. This means that the storage needed varies in size depending on the location and budget. For those tight on space a 1.5m by 1m space is generally more than enough.
For logs the space is larger for the smallest boilers. The boiler is larger, needs more space for a larger flue, and accumulation tank. This is typically 2.5m2
Cost of Fuel
Often the most immediately available fuel is more expensive on the internet. Pellets do range in price, but are frequently £200 per tonne or 4.5p per kWh. (Oil prices were 65p per liter (6.5p per kwh in March and are currently 53p per liter, 5.3p per kWh)
Logs vary more in price and this also varies considerably regionally. For those with a ready supply there is the cost of cutting logs ie your time, or alternatively you can get fuel delivered often at £90-100 per tonne
This makes the cost of logs about half the price of pellets.
Efficiency and Sustainability
A WBS log boiler can be 90% efficient and a pelleburn pellet boiler can be 94% efficient. Some of the efficiency difference can be put down to pellets being dryer and only pulp, ie no bark.
If your logs are from your immediate surroundings then there is no transport or significant processing costs. In addition some pellets have been artificially dried. Whilst not significant, pellets are transported and there is a manufacturing cost that involves drying wood pulp.
If your logs are the result of forestry or woodland management and the wood is offcuts ie cannot be used for other things, then it is sustainable. This is also true for pellets e.g. if as part of making paper there is sawdust and pulp left over then this waste product can make pellets.
There is a strong argument for logs in terms of sustainability and transport. Unfortunately this does not work for many people due to the availability of local woodland management for our homes and logs are not economic to transport.
Renewable Heat Incentive
Currently the non domestic Renewable Heat Incentive pays the same incentive for log boilers as pellet boilers.
A 30kW log boiler May get RHI payments of 30 (Size of boiler) X 8.3 (higher tariff) X 1314 hours = £3271 per annum.
For an installation of logs or pellets costing between £7-10,000 this would payback in under 3 years before you take into consideration the lower cost of fuel.
A Possible Compromise
If you are finding it difficult to decide whether you want logs or pellets. For many the logs do appeal but there is the extra work involved and will you be happy doing this?
The WBS range of log boilers all come ready to fit a pellet burner ie you can convert your boiler over at a later stage. The pp and pelle ranges of burner are easy to fit and with some minor adjustments to your settings you can be burning pellets.
For more information do get in touch with us using the form on the right hand side or by phoning 01225 580 401