Based on numerical simulations detailed information have been gained about the impact of the position of the room temperature sensor in a model room on the energy performance of the space heating or cooling system. Three different ventilation cases (mixing, personal and displacement ventilation) are analyzed. The numerical simulations were performed as coupled calculations of dynamic building behavior and Computational Fluid Dynamics. The simulation model has been validated by measurements in a climate chamber. Generally, higher differences in energy performance could be observed in the cooling case. Both, in heating mode as well as in cooling mode the highest differences can be seen in the case of displacement ventilation. Finally, in the heating mode it is not possible to define an optimal sensor position that fits for all three types of ventilation because optimum sensor position is depending on the installed ventilation system, whereas in cooling mode the optimum sensor position is always the same. In addition it becomes apparent than in all cases and for all sensor positions the criteria of the thermal comfort fulfill the demands of category A, given in ISO 7730.