Carbon dioxide produced by occupants can be used as a natural tracer gas for analysing air change rates in dwellings. However, a high level of concentration uniformity is necessary for tracer gas measurements. Therefore, mixing fans are usually used. The use of such fans in occupied homes is not convenient, thus the uniformity requirement may not be fulfilled. Experiments in climate chambers were carried out to simulate the distribution of CO2 under different controlled conditions, without additional mixing. Sufficient concentration uniformity was observed in all measured cases. Thus, CO2 seems to be well suited for measuring ventilation rates in homes, either during the night when people are sleeping or during the day after the occupants have left the house.