Your Biomass Boiler
To run an efficient biomass boiler you should burn fuel with a low moisture content. Burning wet wood is possible but could seriously affect your boiler’s efficiency. Wet, unseasoned wood fuel, which may be cheaper, will produce more tar and less heat.
Burning wet wood over the long term may seriously affect your boiler’s efficiency, increase maintenance costs and lead to a shorter boiler life. Drier fuel burns more efficiently, without the need to burn off excess moisture.
So it makes sense to burn the best quality fuel in your boiler, just as you put good quality fuel in your car. Currently most wood is purchased on the basis of price and not on the quality, traceability and sustainability of the fuel.
While this isn’t a problem when you buy gas or oil – you buy on price knowing the quality of the product will be standard – it can be a problem when you buy wood fuel. The quality of wood fuel can differ enormously, with many suppliers providing wet chips that will burn less efficiently and cost more in the long run in terms of boiler maintenance and lifespan.
Fuel, Maintenance, and Performance
Biomass boilers are very efficient and can operate at 80-90% efficiency which is considerably better than some conventional boilers. However, all depends on the quality of wood fuel used to power them, whether this fuel is wood pellets, wood chips, or logs.
Issues surrounding the quality of wood fuel usually revolve around
- the moisture content of wood fuel
- the size and quality of wood fuel.
If you do not get the right fuel, then the fuel burns less efficiently, maintenance costs increase, and the boiler’s life is considerably reduced.
The diagram below shows how the calorific value of fuel changes with moisture content. Each type of boiler demands that fuel fed to it falls within a specific range of moisture content. If fuel is fed to a boiler with an incorrect moisture content then it will perform at a sub-optimum level, generating less heat, and so the cost of heat per kWh generated will increase, thereby making biomass less attractive as a heating source.
The table on the right shows the calorific value of wood chip changes, dependent on moisture content of wood chip.
So what does this mean for the price per unit of heat
(kWh) produced? The graph below shows how
variable costs on a per tonne basis of wood chip can
interact with moisture content to produce varying
A key conclusion to draw from all of this
information is that purchasing cheaper
wood does not necessarily translate into
You also need to ensure that the size of the wood-fuel is correct for your boiler. If wood chip is badly chipped then fines, over-size and sub-size pieces will appear which can block the boiler’s augur and combustion chamber. Our wood chips are accredited as to their quality, which means that they have been chipped to the highest levels and less likely to cause mechanical problems in your boiler.
Most smaller boilers require virgin wood with no impurities. Impurities will lead to higher pollution and maintenance costs (and therefore shorter boiler life) due to greater amounts of fly ash. Dry fuel, with low ash content and with minimal impurities will provide you with the most efficiently burning boilers.
By burning dry fuel, you are not only able to reduce your heating costs over the lifetime of your boiler, but can also do so in an ecologically sound manner, as clean virgin wood produces less CO2 than other sources of heat.
* Reproduced with kind permission from the Biomass Energy Centre - ©Crown copyright