Since reduction of ventilation rates in dwellings for economical reasons, it has been necessary to study whether this reduction had not been done to the detriment of indoor air quality. Several means of investigating were developed: experimental tests are indispensable but usually expensive that is why numerous research centres choose to model the thermoconvective fields in rooms. During the last 2 decades, considerable effort has been made to overstep the notion of isothermal air volume because it does not allow to compare heating and ventilating systems, especially with regard to thermal comfort, energy consumption and indoor air quality. The zonal model which is used at the CETHIL (Thermal Physics Centre of Lyon) is a simplified and inexpensive alternative to CFD models which are time consuming and more difficult to apply. This model has been used to assess a ventilation system in which ventilation rate, external temperature and temperature difference between air supply and occupancy zone were varied. The calculations were carried out for the test cell, Minibat, which measures 3.1 x 3.1 x 2.5 (m3). Results were then compared to a campaign of measurements on the real size test cell Mini bat.