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Chopped stacked logs

Log properties


Generally speaking, given their density, hardwood species have a higher calorific value and increased burn time over softwood species by volume, although by weight the two are comparable.

Some of the very dense hardwoods such as oak and elm can be very difficult to burn, so it is usually best to burn them with another type of wood as well. Softwoods tend to be easy to light and will burn quickly, proving ideal fuel for kindling

Most existing log burning equipment can operate effectively on either hardwood or softwood logs, or a mixture. The design of log burning equipment will determine whether it can accommodate hardwood or softwood.


Firewood lengths range from 15-50 cm depending on individual system requirements. Optimum firewood width is between 6-8 cm, if larger than 10-15 cm in diameter logs should be split.

Consistency of log size is important for uniform combustion and to achieve an even burn rate from loading the fire.

Moisture content

The optimum moisture content for logs is 20%, although some modern wood fuel boilers may be able to process wood of a higher moisture content.

Burning logs above the specified moisture content for any wood fuel boiler may result in corrosion of the boiler and chimney, reduced efficiency and generally a lowering of economic return on wood fuel investment.

Contamination/bark content

Wood fuel contamination and/or a high bark content will reduce the burn rate of logs and increase emissions and ash from woodfuel systems.

Sampling and testing

The CEN/TC 355 standards include detailed specifications for sampling and testing biomass fuel.

CEN/TS 355 standards can be downloaded from the Biomass Energy Centre website, as well as further information on standards.