By lowering the pressure in the condenser the energy head to be exploited in the turbine, and with it also the efficiency of the power station, rises. Low condenser pressure means high vacuum. Through leakages (e.g. glands of the low-pressure turbine, flange connections), the concentration of the air in the exhaust steam rises. This air then has to be removed by suction at a suitable point in the condenser. In this report, a calculation method is presented, which enables the two-dimensional simulation of power station condensers. The flow through a condenser can be reparded as a stationary turbulent flow with frictional contact through a porous medium. This flow is described by motion equations, the continuation and the transportation equation for the air concentration. This system is solved by partial differential equations with the help of a Finites-Volumina procedure.