This document defines the specifications and test methods and also the classification, marking and energy labelling of gas-fired instantaneous water heaters for sanitary uses, hereafter called water heaters . This document applies to water heaters: of types A, B and C; NOTE For more information on the configuration of the types of appliances, see FprEN 1749:2019. 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 based on the net calorific value (NCV); with an ignition burner or with direct ignition of the main burner. In this document, the heat inputs are expressed in relation to the net calorific value (Hi). This document 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. This document only covers water heaters where the fan, if any, is an integral part of the appliance. This document is not intended to cover appliances designed and constructed to burn gas containing toxic components.