This standard covering methods for the calculation of system energy requirements and system efficiencies of heating systems in buildings. This standard is to standardise the methods for determining the domestic hot water requirements and the overall methodology for calculation of energy consumption and system efficiencies. It includes calculation of heat losses in the domestic hot water distribution system and in hot water storage units and calculation of energy inputs to the heat generation device producing the domestic hot water. This standard covers the domestic hot water requirements in all buildings.