The analysis presented in this paper is dealing with the correct and energy efficient measures of cooling buildings through nocturnal natural ventilation. Using this solution is proved in this article to be efficient and can reduce substantially the cooling demand. In order to establish the factors influencing the process of passively cooling a building (the ventilation volume, exterior temperature, thermal capacity of the building, possible duration of the ventilation), we have chosen different buildings, which we have placed them in different temperature zones of Romania. The study is based on multiple simulations realized with a time step of one hour, with the following variations: the climatic parameters, the thermal characteristics of the building, the air flow during night time, the proposed interior temperature. Since the study consisted of numerous simulations, in order to treat the results we have used statistical methods that cover the practical and possible situations, and proved the efficiency of nocturnal ventilation.