This European Standard defines the specifications and test methods concerning the construction, safety, rational use of energy and fitness for purpose, and also the classification and marking of gas-fired instantaneous water heaters for sanitary uses, hereafter called "water heaters". This European Standard applies to water heaters: of types AAS, B11, B11BS, B12, B12BS, B13, B13BS, B14, B22, B23, B32, B33, B44, B52, B53, C11, C12, C13, C21, C22, C23, C32, C33, C42, C43, C52, C53, C62, C63, C72, C73, C82and C83, 1); fitted with atmospheric burners; equipped with atmospheric burners assisted by a fan for the supply of combustion air or evacuation of combustion products or fully premix burners; using one or more combustible gases corresponding to the three gas families and at the pressures stated in accordance to EN 437; of nominal heat input not exceeding 70 kW; with an ignition burner or with direct ignition of the main burner. This European standard applies to type C2) water heaters as listed in accordance to Technical Report CEN/TR 1749: types C1, C3 and C5 water heaters including their combustion air supply and combustion products evacuation ducts and their terminal(s); types C2 and C4 water heaters including their connection ducts but without the shared duct system; this shared duct system is part of the building; type C6 water heaters without any ducts; the ducts are separately approved and marketed; type C7 water heaters up to the draught diverter/air inlet but without the secondary flue; type C8 water heaters with their connecting ducts but without the chimney, which is part of the building. In this European Standard, the heat inputs are expressed in relation to the net calorific value (Hi). This European Standard does not contain all the requirements necessary for: boiling water appliances; appliances intended to be connected to a mechanical means of evacuating the combustion products; appliances which fulfil a dual role of space heating and heating water for sanitary use; 1) National installation regulations may specify further requirements and may limit the modes of installation permitted in the territory of a CEN member state. 2) Except for type C6 water-heaters, type C water-heaters are marketed with ducts. Combustion products evacuation ducts in areas of the building other than the room in which the water-heater is installed or ducts or chimneys which are part of the building are also subject to the Construction Products Directive. National installation regulations may specify further requirements and may limit the modes of installation permitted in the territory of a CEN member state. appliances making use of the heat of condensation of the water contained in the combustion products; water heaters of types B21, B31, B41, B42, B43 and B51; This standard only covers water heaters where the fan, if any, is an integral part of the appliance. This European Standard: does not apply to appliances not intended to be connected to a flue when they are not fitted with an atmosphere sensing device; takes account of the information given in Technical Report CEN/CR 1472 with respect to marking; only covers type testing. Matters which relate to quality assurance systems, production tests and the certification of auxiliary controls are not dealt with in this European Standard.