Space heating and hot water supplying are usually done by utilizing combi boilers. Various kinds of combi boilers are available. In the last years condensing type combi boilers have been introduced that have high efficiency in comparison to conventional one. In the present study the impact of combi boiler type on pollutant gas emissions was experimentally investigated. Three various combi boiler including condensing, full condensing and conventional type combi boilers have been utilized in the experiments. Moreover, the experiments have been conducted in various outlet hot water temperatures to determine the effect of temperature. The achieved findings indicated that in all temperatures utilizing condensing and full condensing combi boilers decreased NO, NO x and SO 2 , gas emissions considerably.