This European Standard specifies the structure for calculation of energy use for space heating systems and domestic hot water systems in buildings. It standardises the required inputs and outputs for the calculations, in order to achieve a common European calculation method. The calculation method facilitates the energy analysis of the different sub-systems of the heating system, including control (emission, distribution, storage, generation), through determination of the system energy losses and the system performance factors. This performance analysis permits the comparison between sub-systems and makes it possible to monitor the impact of each sub-system on the energy performance of the building. Calculations of the system energy losses of each sub-system of the heating system are defined in subsequent standards (prEN 15316, parts 2-x, 3-x and 4-x). The system thermal losses, the recoverable system thermal losses and the auxiliary energy of the sub-systems of the heating system are summed up. The system thermal losses of the heating system contribute to the overall energy use in buildings (prEN 15603). Ventilation systems are not included in this European Standard (e. g. balanced systems with heat recovery), but if the air is preheated or an air heating system is installed, system energy losses of these systems are covered by this European Standard.