This European Standard is applicable to solar supported gas-fired appliances producing domestic hot water. It applies to a system marketed as single unit or a system fully specified by a manufacturer that: - has a gas heat input not exceeding 70 kW; and - has a hot water storage capacity not exceeding 500 l; and - is equipped with at least one solar collector; and - is, with regard to the solar hydraulic circuit, considered as a forced circulation system (definition according to EN ISO 9488:1999). The appliances covered by this European Standard are described in Annex C. This standard does not apply to thermo-siphon or integral collector storage systems (definitions according to EN ISO 9488:1999). In principle, the energy consumption of thermo-siphon solar preheat systems and integral collector storage preheat systems can also be assessed on the basis of this standard. One appropriate procedure for that purpose is to calculate the temperature level of the domestic hot water withdrawn from the thermal solar system for the reference conditions defined in this standard by using the numerical system model and the thermal solar system performance parameters according to ISO 9459-5. Based on the temperature level of the hot water withdrawn from the store, the energy consumption of the gas appliance should be determined. This determination can either be done by means of calculations or by performing a test according to EN 13203-2 and using instead of the cold water inlet temperature the hot water temperature withdrawn from the store. This standard is not intended to assess the performance: - of the solar collectors, which should comply with EN 12975-1 and EN 12975-2; and - thermal solar systems and components, which should comply with EN 12976-1 and EN 12976-2. This European Standard, EN 13203-3, sets out a method for assessing the energy performance of a solar supported appliance. It gives a number of daily tapping cycles for each domestic hot water use, kitchen, shower, bath and a combination of these, together with corresponding test procedures including information about the available solar radiation. It enables the energy performances of different gas-fired appliances to be compared and matched to the needs of the user. The Committee responsible for this standard is NA 032-03-01-03 AK "Spiegelausschuss CEN/TC 48/109" ("Mirror Committee CEN/TC 48/109") at DIN.