From the beginning of 2006 all new European buildings (residential, commercial, industrial etc.) musthave an energy declaration based on the calculated energy performance of the building, includingheating, ventilating, cooling and lighting systems. This energy declaration must refer to the primaryenergy or CO2 emissions. The European Organization for Standardization (CEN) has prepared aseries of standards for energy performance calculations for buildings and systems.This paper presents related standards for heating systems. The relevant CEN-standards arepresented and a sample calculation of energy performance is made for a small family house. Theadditional heat losses from heating systems can be 18-25% of the building energy demand. Theadditional loss depends on the type of heat emitter, type of control, pump and boiler. The mostimportant losses for floor heating were in the emission system. The most important losses for radiatorswere in the distribution and generation system.