A model is presented for computing the infiltration and airflow between rooms of a multiroom building in terms of basic principles of fluid mechanics. This model has been incorporated into a comprehensive loads-predicting computer program. Airflows, room temperatures, and heating loads for a typical townhouse under different conditions of environment and with various construction features are computed. These calculations show the feasibility of detailed multiroom air movement analysis. They also indicate that when the interroom openings of a lowrise structure are large compared to the envelope openings, the infiltration and total load can be accurately and more quickly computed by assumming no resistance to airflow between rooms. This property will also allow simplified calculations for high-rise buildings with many rooms. Methods are proposed for handling more complex airflow phenomena.