This European Standard covers direct-fired steam boilers and hot water generators, including the auxiliaries. For the purposes of this standard, steam boilers and hot water generators are vessels and pipework systems in which: - steam at a pressure higher than atmospheric pressure is generated for use external to the system; - water is heated to a temperature higher than the saturation temperature at atmospheric pressure for use external to the system. A steam generator normally consists of the flue gas-heated evaporator, the superheater, the reheater, the feedwater heater, the air heater, the fuel heater, if any, and the fuel burning equipment. The term 'direct-fired' relates to equipment by means of which the chemical heat in the fuel of known composition is converted to sensible heat. Such equipment can involve stoker firing, fluidized-bed combustion or burner systems. The auxiliaries include the fuel feeders, the pulverizer, the FD (forced draught) fan, the ID (induced draught) fan, the facilities for removal of the refuse (combustion residues), the steam air heater, the main air heater, the fuel heater, if any, and the dust collector.