High levels of indoor relative humidity are one of the main causes of moisture damage in buildings. That cause can be removed by an appropriate ventilation system. Relative humidity controlled ventilation systems were designed to increase energy performance of buildings without exposing them to moisture damage. The study of the performance of such a system in terms of energy savings and maximum relative humidity is proposed here using numerical simulations with an appropriate whole building heat, air and moisture modelling approach that is developed in the frame of IEA Annex 41. In the studied dwelling the benefits of relative humidity controlled ventilation system were found only in terms of indoor climate (relative humidity) and not in terms of energy savings. Moreover the study showed that for the predictions of global energy consumption some simplifications, such as using monozone calculations and neglecting moisture buffering effect of materials can be admitted. However for estimations of the indoor climate in each room (temperature and relative humidity) multizone simulations and modelling of moisture interactions between air and materials are necessary.