The scope of this general part is to standardise the required inputs, the outputs and the links (structure) of the calculation method in order to achieve a common European calculation method. A common calculation method will help to facilitate the free circulation of services (optimisation of the energy performance, display of conventional level of energy requirements) and products (software). Ventilation systems are not included in this standard (e. g. balanced systems with heat recovery), but if the air is preheated or an air heating system is installed, system losses of these systems are covered by this standard. The energy performance may be assessed either by values of the system efficiencies or by values of the system losses due to inefficiencies. The calculation method is based on an analysis of the following parts of a space heating and domestic hot water system: the emission system energy performance including control; the distribution system energy performance including control; the storage system energy performance including control; the generation system energy performance including control (e. g. boilers, solar panels, heat pumps, cogeneration units). The energy required for the heating system is calculated separately for thermal energy and electrical energy in order to determine the final energy, and subsequently the corresponding primary energy is calculated. Calculation factors for conversion of energy requirements to primary energy shall be decided on a national level. The specific calculation algorithms or tabulated input values for the calculations of each part of the space heating and domestic hot water system (i.e. emission system, distribution system, storage system and generation system) shall be specified in subsequent standards referring to this standard or in national annexes.