This European Standard applies to type CX3 central heating boilers as specified in 4.1, equipped with atomizing oil burners: – type C13, type C33, and type C53 boilers, including their combustion air supply and combustion products evacuation ducts and their terminals; – type C43 boilers including their connection ducts but without the chimney which is erected as a shared duct system and which is part of the building; – type C63 boilers, including the connecting piece as specified in 3.7, if not integrated into the boiler; – type C83 boilers, including their connection ducts but without the chimney which is part of the building; – that have a nominal useful heat output below or equal to 70 kW; – where the temperature of the water does not exceed 100 °C during normal operation; – where the maximum water-side operating pressure does not exceed 8 bar. This European Standard is intended to establish specific requirements and test methods for type C atomizing oil burning central heating boilers with respect to construction, safety, fitness for purpose, rational use of energy, classification and marking. This European Standard covers only standard tests. For boilers that produce domestic hot water by a drum or a heat exchanger, integrated or juxtaposed, (by accumulation of instant production), this standard only applies to hot water reheating system components that are not subject to operating conditions applicable to the boiler heating system. This European Standard covers units consisting of boilers equipped with burners that meet the requirements of EN 267, with the following exceptions: – maximum NOx and CO emission values, estimated for boilers according to the classes defined in EN 303-2; – air factor value, defined by the manufacturer and stated in the boiler’s technical specifications; – marking and/or burner data plate which may provide information for the boiler data plate; – installation recommendations for installing the burner on the boiler included in the boiler operating instructions. This European Standard modifies EN 303-1, EN 303-2, EN 304 and specifies supplementary requirements only for room sealed operations.