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The hourly dynamic calculation method given in EN ISO 13790 uses a lumped-capacity 5R1C thermal network model of a building. This model enables the use of hourly occupancy patterns. But introduction of hourly ventilation schedules is not recommended because in some equations of the calculation procedure division by zero appears when the infiltration and ventilation airflows are zero. This paper presents a modified 4R1C version of the 5R1C model. The existing ventilation heat transfer was replaced by the new heat flux modelling the time varying airflow due to infiltration and ventilation. The calculation method to obtain heating and cooling power required to maintain internal set point temperatures was presented in details. The new model was validated against EN 15265 with the error up to 6.7% and 5.4% for heating and cooling, respectively. Only in the test 10 for heating the error was 31.6%. BESTEST tests were passed successfully, except for the minimum annual temperature of −19.3°C which didn't fall within the reference range in the test 600FF. In simulations of the single family building the coefficient of determination of the calculated internal operative temperature and thermal power against reference EnergyPlus results was R2 > 0.844 and R2 > 0.811, respectively. [ABSTRACT FROM AUTHOR]