In this paper we present a model for predicting air infiltration that eliminates many site-specific parameters normally required. The only information necessary is the geometry and leakage of the structure. The leakage quantities, expressed in terms of effective areas, are total leakage area and the leakage areas of the floor and ceiling. Weather parameters are mean wind speed, terrain class, and average temperature difference. The model separates the infiltration problem into two distinct parts: stack and wind-regimes. Each regime is treated independently; the transition between them is sharp. The model has been tested with data from several sites, differing in climate and construction methods.