The energy use in buildings is dependent on the choices made during the design, construction and renovation. The causes for these differences are, among others, caused by the behavior of the occupant of the building and the choice of heating and ventilation system. The European scheme of Energy Performance Certificates (EPCs) aims at reducing the energy use in the built environment. It is most common to calculate (i.e. not measure) the energy use for the buildings which are affected by the scheme. In Sweden, on the other hand, the EPCs are normally based on measurements of the actual energy use in the building. This makes comparisons between calculated energy use for building permit and measured energy for EPCs possible. In this paper a study of the differences between the calculated and measured energy use and its correlation with the choice of heating and ventilation system is presented. This is done by detailed investigations of the calculated and measured energy use in 44 buildings. For further analysis, a database of 1 753 buildings with measured energy use (EPCs) is used to study the dispersion in energy use for buildings with different heating and ventilation systems. Analysis using numerical simulations tools on human behavior has also been performed. The results of the investigation can be used to further improve the measured EPCs.