This paper presents the development of a three-dimensional numerical model to study the distributions of indoor air velocity, air temperature, contaminant concentration, and ventilation effectiveness in a two-zone enclosure. The numerical model is based on the k–ε two-equation model of turbulence and the SIMPLE algorithm. The false-time step and ADI iteration procedure are employed. The results of the computed velocity and temperature profiles and convective heat transfer by the model are in good agreement with the measurements as well as with the prediction of the PHOENICS code.