This European Standard specifies a method for the energy assessment of a domestic/sanitary hot water storage tanks of up to 2 000 l. Whilst water heaters intended primarily for direct heating are not covered by this European Standard, it does allow the provision of electric heating elements for auxiliary use. Primary heating buffer tanks are not covered by this standard. Heat losses of domestic hot water storage tanks integrated into liquid fuel combi boilers marketed as a single unit are tested according to EN 303-6.