Sets out a method for calculating the energy consumption of electric storage water heaters fitted with electric resistance heating units. This Standard is not applicable to gas water heaters, solar water heaters, heat-exchangers or heat-pumps. The Standard is based on known performance characteristics of electric storage water heaters under static conditions (i.e. standing heat losses with no deliver) and using an energy delivery of 37.7 MJ per day (equivalent to a volume of 200 L of water raised in temperature by 45 C).