Moisture Content

The majority of biomass boilers are designed to burn wood chip with a maximum level of moisture in it. This moisture content can vary from 25% to 60% but is most typically at 35%. The levels specified by the boiler installer company will vary according to the make, style and size of the boiler and its fuel transfer system.

If the moisture content of the wood chip is too high it can cause a boiler to shut down, while if it is too low and the wood chip is too dry it will burn too quickly.

Having a reliable supply of high quality wood chip at the correct moisture content is probably the most significant factor affecting the operation of a biomass boiler.

Forest Fuels screens and tests its wood chip to ensure that we always deliver premium grade fuel at the correct moisture content.

Freshly cut ‘green’ timber and tree surgery wastes will have much higher moisture content than clean recycled wood chip. The art is in air drying and blending any wood chip to reach the desired moisture content.

The table below provides an indication of the link between price per tonne and pence per kWh for wood fuel at different moisture contents. Forest Fuels Ltd aims to deliver wood chip at 25-30% moisture content to most biomass boilers unless they are wet fuel boilers.

Graph courtesy of Econergy.