The COMIS program for modelling air flows inside buildings has been modified to allow individual rooms to be divided into smaller (sub-) zones. This extends the model to enable predictions of variations in temperature distributions and air flows within rooms. The new program has been evaluated by comparison with published experimental measurements and with the results from other zonal and computational fluid dynamic (CFD) models. The comparison indicates that this new program is an effective model for predicting air flow and temperature distribution within buildings.