The goal of this study was the determination of the existing situation in houses with regard to air quality and energy used for ventilation in relation to the health of inhabitants. For the energy policy the Government is considering increased energy requirements for dwellings. They are permanently opposed in doing so by people who are concerned about negative health effect due to increased requirements on for instance air tightness of buildings. To have at least a reference point, they are interested in the existing situation. The objective was to get information for houses on: - existing air quality - the relation between IAQ and the way inhabitants use their houses, including the use of the ventilation provisions - the air tightness of the houses - the real temperatures - other parameters determining the energy performance The set up of this project was: - an enquiry in 1000 houses which should be as representative as possible for the Dutch housing stock concerning the ventilation, comfort and some health related aspects - measurements in about 100 houses on ventilation and temperatures during a whole heating season and the air tightness - detailed measurement in 10 houses on IAQ, ventilation, temperatures and energy related parameters, to get information on the distribution over time In this publication there is no results of the details measurements are given. The reason for this is that not all analysis have yet been done.