In order to save energy, i.e. ventilation heat losses, the fresh air change rate should be adapted to the prevailing need. Even though it is a fact that reducing the fresh air change rate will result in a ventilation heat gain, the fresh air flow rate should not be kept too low, so that pollutants, humidity and body odour can accumulate. The results of measurements in a climatic chamber and in a lecture theatre show a significant relationship between the concentration of carbon dioxide and body odour of the indoor air under nonsmoking conditions. The upper limit of carbon dioxide, where the indoor air quality is still acceptable to persons entering a room, is between 0.1% and 0.15% vol, whereas for occupants in the room this limit is higher because of adaptional effects.