This paper presents the results from an experimental investigation of wood combustion. Variables chosen for investigation are fuel moisture content, fuel particle size, excess air, fraction and temperature of under-fire air. Influence of the off-design (part load) operation of the combustion unit on combustion efficiency and particulate emission is also investigated. Data recorded during the experiments include the composition and temperature of the combustion products, particulate emissions, and combustible fraction of the particulate. Based on the experimental data, a linear regression model was developed to investigate the variables affecting the combustion process. A computer model was used to calculate the temperature and composition of the combustion products under adiabatic conditions. Results of the adiabatic model and the experimental regression analysis are compared and discussed. According to the results presented, it is concluded that the combustion efficiency and particulate emissions are most influenced by the factors that increase the volume of the combustion products in the combustion chamber. These variables include excess air, moisture content of the fuel, and the combustion air temperature. Fuel particle size and the fraction of under-fire air did not significantly affect the combustion efficiency and particulate emissions. It is also concluded that the off-design (part-load) operation of the combustion unit, results in higher particulate emissions and lower combustion efficiency.