The aim of the study was to examine the impact of wood pellets of different type on the emission of nitrogen oxides (NOx) formed during the combustion process in a low-power heating boiler. The study aim was to determine the dependencies of NOx emission levels on the chemical composition of fuel. The test was carried out using a model of a combustion chamber equipped with a dedicated burner. Analysis of the results confirmed, the relationship between flue gas and the formation of NOx. The obtained results prove the possibility of reorganizing the combustion process in order to reduce NOx emission by selecting a proper composition of raw materials when producing wood pellets.