Bark contains a high mineral content compared to stem wood which leads to high ash formation and potentially slag and clinker formation (ash that melts).

Sawmill offcuts too contain a high proportion of bark.  While these are all potentially good biomass fuel, the high ash content may make it unsuitable or undesirable for some systems, especially domestic and small scale systems.

Larger scale systems are likely to have fewer problems with this and specially designed bark boilers can be installed to use this valuable residue to generate process heat for timber drying kilns on site.

Sawdust from sawmills, especially dry sawdust from sawing kiln dried timber, is potentially highly suitable for wood pellet production.

Small scale pellet presses designed to be used alongside sawmill operations are available in the UK, and a portable pellet press that can travel to small sawmills with insufficient capacity to justify a dedicated press may be another alternative.