What is the calorific value of logs?
Around 5kWh per kg, depending on moisture content and type of wood (hardwood or softwood, and species). For a batch-burning boiler, the ideal size is 50cm in length, 12-15cm in thickness.
What kind of logs should I burn?
Logs should be sustainably sourced, seasoned for between 1-2 years to ensure below 20% moisture content and fuel that is free from coatings and preservatives. Unseasoned or wet logs burn inefficiently, reducing the heat produced, and instead produce excessive soot and tar which can cause flue fires. Moisture levels are best tested with a handheld moisture meter.
How long do logs take to dry?
Hard woods will take longer to season (two years) than soft woods (one year).
Where can I find a good log supplier?
The Biomass Suppliers List (BSL) includes the most comprehensive list of high quality wood fuel suppliers in your area.
The table below compares logs and other forms of heating fuel.
Biomass fuel information
Information about the different fuel types available for biomass boilers, the regulations, considerations to take and information on procurement.
Wood chips are small pieces of logs or wood waste. These are formed by passing through a chipping machine, which turns them into 30mm pieces, also known as G30.
Wood pellets are a type of biomass fuel, made from compacted sawdust or other waste from saw-milling and manufacturing. At 4.8kWh per kg, you only need one third of the space that you'd need for wood chips.
As a biomass fuel, logs will generally deliver 5.1kWh per kg, depending on moisture content and type of wood (hardwood or softwood, and species).
Grain can be an economical and convenient fuel for use in biomass boilers. 'Pourable' grain such as oats, wheat and barley have a low nitrogen content. Being a slightly denser fuel than miscanthus, it will require less space to store for the same amount of heat.
Miscanthus, (or 'elephant grass') is a perennial grass originating from Asia. It is becoming popular as an energy crop as it can easily and quickly grow on poor quality land with no need for fertilisers or very much intervention.
About the BSL
The Biomass Suppliers List (BSL) is a list of woodfuel that has proven it meets the eligibility requirements for the Renewable Heat Incentive (RHI) scheme.