Describes a simplified numerical model, POMA (Pressurized zOnal Model with Air-diffuser, intended to predict the airflow pattern and thermal distributions within a room. The authors introduced jet characteristic equations into the model to make its application general for mechanically ventilated buildings. The models prediction was compared with experimental results and with that of another zonal model and a CFD model. Both natural and forced ventilation were considered. States that the findings show that the POMA model is a practical tool for ventilation system design.