At the beginning of the paper, the steam oil generator is described, as well as the thermal oil it uses. Also, the shell and tube heat exchanger are described, on the basis of which the design of this steam generator works. Boilers that have a similar purpose to generators are also described and compared to show the differences. A mathematical model has been created, through which, with known input data, output quantities such as heat flow, mass flow, number of pipes, pressure drop inside the pipes and the like are obtained. A code was created for the mathematical model in the Engineering Equation Solver (EES), through which the results were obtained. Also, using EES, the influence of input variables on output results is shown in order to understand how each variable affects the heat exchanger. In the end, a proposal for a construction solution was given, which still needs to be refined in detail with the construction office and technologists. It is described how the commissioning of the steam generator should look like, as well as the pressure test of the same. In conclusion, steam generators with shell-and-tube heat exchangers are widely used in industrial processes. The calculation gives the necessary heat flow for evaporating water to dry saturated steam and other results in order to make a high-quality steam generator. With proper use and maintenance, it contributes to the efficiency and economy of the entire system and prolongs its service life.