Combustion processes in a biomass bed are investigated experimentally. Special attention is paid to the influence of primary airflow and particle properties on the ignition front, its temperature and on the composition of the gas leaving the front. Two test rigs have been built: a large rig in the same size as a boiler for domestic use and a small laboratory test rig. In both rigs the ignition front moves in opposite direction to the primary airflow. Three combustion regimes are identified: a sub-stoichiometric regime with incomplete consumption of oxygen, a sub-stoichiometric regime with complete consumption of oxygen and an over-stoichiometric regime. The results show that a fuel with higher density and thermal conductivity (but in other respects similar to other fuels) has a wider sub-stoichiometric regime where oxygen is cornpletely consumed. If the particle size is increased (for the same fuel quality) the airflow range of this regime becomes shorter and starts at higher airflow.