In the present paper, first results of an extensive and ongoing parametric study are shown. The objective of the parametric study is to clarify the influence of relevant flow and geometrical parameters on the microclimate and thermal comfort of the occupants. Flow parameters included in the study are air mass fluxes, velocity magnitude, air temperature and inflow direction at the vents. Geometrical parameters of interest are number, location, area and shape of the air vents as well as geometrical details of the passenger compartment itself.The parametric study is performed numerically on the basis of a computational model for a passenger compartment of a Mercedes E-Class sedan. The numerical method used has been published earlier and consists of a system of three programs for simulating the flow and temperature field in the cabin, the heat transfer and radiation and the thermal sensation of the occupants.The special focus of the present paper is on the influence of the area of the side and center vents as well as the air mass flux distribution at these vents for summer climatic conditions. The results show a significant influence of the vent areas not only on the velocity levels in the passenger compartment but also in the overall flow topology. The global and local thermal comfort values strongly depends on both parameters, vent area and air mass flux. Uncomfortable air draught can be observed at the head of the frontal occupants for to small vent area, but can be reduced by changing the mass flux distribution at the vents. As a long term objective, it is hoped, that the results of the parametric study can lead to some general design guidelines, which could be used in an early stage of the development process of a new car.