We also evaluated that buildings using a district heating system (average = 77 kWh/(m2a)) or a pellet boiler (aver- age = 63 kWh/(m2a)) consume less thermal end energy. Particularly due the small number of pellet boilers used in low-energy or passive school buildings, it was concluded that the reason for these buildings' lower energy consumption does not depend on the energy source but rather on the building's energy standard. Contrarily, the buildings with higher energy consumption still use fuel oil boilers (average = 149 kWh/(m2a)) and are, generally, older buildings (more than 10 years old) or extensions of existing buildings supplied with heat from the older main building. Hence, it is not the energy source which is determining but the practice and intention of the building owners which have changed in recent years.