To estimate "real conditions" emission factors for residential boilers used to supply central heating systems and/or domestic hot water preparation, boiler's daily heat balance was used, incorporating the individual phases of its operation. For this purpose emission factors of gaseous and particulate pollutants were measured for each phase of daily cycle of the boiler. Three types of modern devices have been tested, i.e. automatic boilers fired with coal and pellets and gasification boilers with manual loading of wood logs. An analysis of characteristic parameters and settings of boilers that affect the emission values in particular phases was also carried out. Based on the daily energy balance of each boiler type, the daily operating regime of these devices in real conditions was established and the duration of individual phases was estimated. Finally, using the obtained data and statistics describing the use of individual devices, the emission factors describing the operation of the boilers under interest, were determined. Modern manual boilers had very high carbon oxide and organic gaseous compounds "real-life" emissions (2100 and 160 g/GJ, respectively) which were 4.2 and 10.4 times higher, respectively, than Ecodesign requirements. Ecodesigned automatic pellet boilers were the least polluting in terms of all investigated compounds. For this group of devices, the Ecodesign limit values were exceeded only for carbon monoxide (430 g/GJ), mainly due to the "real-life" cycling between heat outputs and combustion phases.