The main purpose of this work is to model a high-rise building during the winter period by mean of COMIS regarding to the airflow patterns at each level of the building so that to predict the stack pressure which causes many problems which are the energy loss, the sticky elevator doors and the loud noise at lobby entrance. The present building which is situated in Korea contains 30 floors above the ground level and 5 basement floors. Using COMIS, we have first modeled the entire building. However, the simulation failed due to the huge number of zones and interactions between them. Therefore, a reduced model of the present building which contains 19 floors with 5 floors in the basement has been decided. A simplified model based on the reduced one has been constructed and compared with the reduced one. The result of the simulation shows that this approach could be used with accuracy still being satisfied. The simplified procedure has been extended to the high rise building model with 30 stories above the ground level and 5 stories in the basement. The effect of some intrinsic parameters on the stack pressure and the airflow patterns in the shaft elevators has been investigated.