The specific weight of biomass and pellets in thermal energy production recently started to increase rapidly. Continually growing price of fossil fuels and European Union requirements to increase renewable energy in thermal energy production are the main reasons of biomass specific weight increase. Unfortunately Latvia uses only a small part of the country's existing biomass potential for the time being. The growth of the amount of the biomass utilisation for energy production can be foreseen in the future, because such type of energy production has a number of advantages, one of which is lesser amount of emissions that arise during the combustion process. However, the amount of emissions that arise during the combustion of wood pellets can get lower due to the optimisation of combustion process. Air supply is one of the main factors which have effect on the heat loss, boiler efficiency and emissions levels. The main goal of this study is to optimise pellet combustion process in small scale pellet boiler due to the air supply improvement. Experimental research of the combustion process of pellet boiler with nominal capacity 25 kW was carried out during the work. First at all, the effect of changes in the amount of air supplied to the boiler combustion process was determined. Then approbation of two methods for combustion process improvement has been made. The first method was based on the flame dissipation, but the second method included the opposite method - flame concentrating. However, the main task of both methods applied was to improve the process of mixing air and fuel. It was important to reduce the rate of air supplied, too. Four different gratings were used for dissipation of the flame. Cylinders without and with a spiral for flow swirl were used for flame concentration. The results of the study show that both methods in general have positive impact on combustion process.