The passive cooling techniques such as night time cross ventilation is potentially an interesting strategy to provide substantial cooling energy savings in warm climates. The efficiency of the night cooling ventilation is determined by three main factors: the external air flow rate in the room, the flow pattern and the thermal mass distribution. Most of the software used to simulate building thermal performance assumes natural convection in the enclosure; therefore the convective heat transfer coefficients for internal room surfaces are underestimated. The aim of this paper is to analyse the effect of the enclosure shape and the inlet/outlet openings situation on these convective heat transfer coefficients. This analysis allows a comprehensive sample of typologies to generate guidelines which can help the designer with the distribution of the thermal mass and inlet/outlet openings in the enclosure. The approach will combine a theoretical analysis to characterize globally the enclosures getting charge/discharge time constants with simulation studies based on computational fluid dynamics software.