The diploma thesis is focused on the design of heating of the digestion tank, which is part of the waste water purification process and where the process of sludge digestion takes place. Anaerobic digestion (methanisation) is a process main goal of which is the hygienesation of incoming sludge and related biogas production. In the first part the reader is introduced to the subject of mixed and heated industrial vessels. In the second part of the thesis thermo-hydraulic calculation of the heating process is carried out in case the vessel is agitated and in case the agitation is not applied. The next part of the thesis describes the procedure for creating a calculation tool, which is later used to solve two sample problems. The last part desc...