Due to the increase in CO2 emissions and the resulting climate change more and more efforts aremade to reduce energy consumption. As a result, the energy demand of buildings is to be reduced by specific measures, for example thermal insulation or intelligent ventilation systems. A demand-based (moisture-controlled) exhaust ventilation system is assessed in comparison to a supply and exhaust ventilation system with heat recovery by means of computational investigations. This assessment of different ventilation systems is performed by means of the newly developed hygrothermal indoor climate simulation model WUFI-Plus. By implementing the individual ventilation systems the energy demand, especially the primary energy consumption on the basis of applying various fuels, as well as the effects on the indoor climate and the CO2 content of the indoor air are calculated and compared. Moreover, air change rates are investigated resulting from the use of a demand-based exhaust ventilation system. The calculations are based on a model apartment with a ground floor of 75 m2 and an assumed 3-person household. These investigations comprise 3 different climates in Germany (cold, medium and hot climate).Despite the high heat recovery coefficient of the supply and exhaust ventilation system an only slightly higher energy use occurred for the demand-based exhaust ventilation system. If regenerative energy sources such as wood are used, primary energy consumption of the demand-based exhaust ventilation system is even lower in comparison to the supply and exhaust ventilation system with heat recovery. With demand-based exhaust ventilation system, the CO2 concentration of the indoor air remains permanently below 1200 ppm.