For natural gas, chemical composition given in Table 1.1, a design of a steam generator was prepared. First, the quantities related to the combustion process of a given fuel, the amount of fuel, the actual amount of combustion air, the actual amount of dry and wet flue gases and their total amount and composition were established. The results are combined with combustion diagrams and H-t flue gas diagram, which are the basis for further calculation. After that, the heat losses of the steam generator related to fuel efficiency, combustion efficiency and the total efficiency of the generator itself were calculated, on the basis of which the total fuel consumption of the entire system was obtained. A further calculation established the process state values for the given input data according to the tables of superheated and saturated water vapor, on the basis of which the transferred heats on individual heating surface generators were calculated, ie in water heater, evaporator, steam superheater and air heater. These values were used in the calculation of heating surfaces and the calculation of the firebox. The calculation of the firebox consists of the calculation of the main dimensions and the calculation of the irradiated area. Calculations of heating surfaces consist of the calculation of the average logarithmic temperature according to the differences of the media at the inlet and outlet of an individual part and the calculation of the heating surface according to certain heat transfer coefficients. A calculation was made firmly for the same parts of the steam generator, ie in the places where the largest volume occurs, for the selected material 13CrMo45. Therefore, it was concluded that the stresses are less than allowed at a given pressure and dimensions and that the calculation is firmly satisfied.