Stage 1 requires the combustion chamber to
be hot above and around where the fuel enters
the grate. Most biomass boilers contain some
refractory material for this reason. Boilers
designed to burn wet wood chips have substantial
refractory linings in large combustion chambers.
The greater the quantity of refractory lining, the
less responsive the boiler to changes in heat
demand, the longer the time taken to reach
ignition temperature and the greater the residual
heat that will need to be dissipated when the
boiler is switched off.