Past decades tightening of building regulations with regard to energy consumption have reduced the heat loss through the building envelope and the buildings have become more airtight. The importance of having a well designed and functioning ventilation strategy in new buildings is therefore essential in obtaining an acceptable indoor air quality and avoiding damage to the building due to mould growth etc. The EU directive on the energy performance of buildings has been introduced to promote improved energy performance of buildings taking into account the outdoor climate and local conditions, as well as the indoor environment requirements and cost effectiveness. Ventilation of the building takes up a considerable amount of a buildings energy consumption however research have showed that it is possible to reduce the energy loss by ventilation when using a demand controlled ventilation (DCV) system in residential buildings. Analysis of a DCV system in residential buildings will be performed, and the paper will present the investigations and discuss aspects of DCV systems with regard to air quality and energy savings.