Biomass boilers take their energy from burning biomass fuel; the fuel consists of organic matter that does not include fossil fuels. The boilers can be used as a direct replacement for an existing oil/gas boiler, although thought must be given to the storage requirements of the fuel needed.

This system is only 90-95% efficient, but because the fuel is total sustainable and the boiler needs only negligible electric to run, this form of heating is classed as carbon neutral.