internal air flows due to ventilation through large openings is an integral part of the ventilation and energy design of buildings and should be taken into account among other thinks in the simulation of occupants' behavior. In this paper, the effect of the arrangement and use of the internal openings in a two-storey house on the interzonal flows inside the building's rooms is examined, with the aid of nodal ventilation modeling. Validation experiments are also performed for a series of arrangements of internal and external openings, by conducting tracer gas measurements. A parametrical investigation is carried out for selected parameters, including the effect of the percentages of the windward and leeward openings on the interzonal flows, monitoring magnitude and direction changes, for specific climatic conditions. Conclusions about interzonal flows and ventilation design are drawn. (c) 2004 Elsevier B.V. All rights reserved.