Abstract Flames of mixed wood, sawdust, fermentation-process residues and grain residues have been fired at 15 kW thermal input to determine flame ignition, temperature levels, NOx emissions, combustibles burnout as well as fly ash slagging propensity. South African Middleburg coal has been combusted under similar conditions. Near the burner, the in-flame temperatures of the coal flame are around 100 °C higher than in the biomass flames and the fastest ignition has been observed for the coal flame. Combustibles burnout is good, exceeding 94.2% for all the fuels. For mixed wood and saw dust, around 50–60% of the fuel nitrogen has been converted to NO whilst for the fermentation and grain residues as well as for the coal, the nitrogen conversion rates are in the 14–18% range. Ash deposition experiments have been carried out in the 950–1200 °C temperature range. Around three times more deposit (when normalized to the fuel ash content) is formed for biomass fuels than for the coal. For biomass fuels, a good correlation between deposition rate and particles temperature has been obtained. Sticking efficiency of the impacting particles has been estimated to be 0.03–0.09 at 970 °C and around 0.4 at 1170 °C.