The main objective of this study was to conduct the combustion process of selected wood fuels in a low-temperature bottom-combustion water boiler, while analyzing combustion gases for the presence of CO, NOx, and SO2 at respective combustions stages. In research conditions, substantial CO, NO, and SO2 emissions to the atmosphere were observed, especially during the combustion of fuels characterized by finer grains (sawdust) and susceptible to the evaporation of volatile content-coniferous-tree wood. Nevertheless, the first and third stages of combustion when using biomass for power generation, under counter-current combustion conditions in bottom-combustion boilers, are accompanied by problematic emissions-mainly of CO. Therefore, such heating devices require an improved airflow, and, in the case of using an electronic combustion controller, more-precise algorithms controlling airflow to the boiler should be devised.