In the introductory part, the main function of the heat exchanger is described and the ways of their application are listed. Heat exchangers are then divided in many groups, according to geometry of construction, transfer processes, etc. Shell-and-tube heat exchanger and its geometry parameters are described in detail. The following is the sizing of the shell-and-tube heat exchanger according to the given problem. A preliminary estimation of unit size is first approached to obtain approximate characteristics that will give guidelines for selecting the appropriate shell diameter, etc. The sizing is performed according to the mathematical model of the heat exchange process in the heat exchanger, which was defined earlier. A design rating is performed by examining the geometry parameters of the heat exchanger. The influence on the exchanged heat transfer rate is examined, and the geometry parameters that are being changed are tube layout, baffle number, the number of tube passes, the tube diameter and tube length. A higher heat transfer rate and a higher overall heat transfer coefficient are achieved by a triangular pitch (compared to a square pitch), by increasing the number of baffles (reducing the baffle spacing) and by increasing the number of tube passes. Average velocity inside tubes increases in the case of higher number of tube passes, and decreases if larger tube diameters are selected. By increasing the tube length, heat transfer area and heat transfer rate are increased.