In this study the thermodynamical behaviour of the refractory lining of three different scrap melting furnaces operated at their typical melting temperatures for steel, copper and aluminium is determined and compared. The furnaces examined are an electric arc furnace for steel, a reverberatory melting furnace for copper and a top-charge melting furnace for aluminium. The primary aspects which are investigated are the operating processes of the individual furnaces as well as the general design of the refractory lining, while paying special attention to the thermal properties of the refractory materials. The steady state temperature profile and heat transfer through the refractory lining of each furnace is computed, as well as the magnitude of the stored enthalpies of the lining respectively the melt and their relationship to each other. This is investigated for the new and also for the worn lining. Furthermore the transient temperature profiles during the heating-up process of the lining are determined via the finite-difference-method, applying typical heating-up curves as usually applied in industrial furnaces as boundary conditions. Finally the impact of short term temperature drops at the hot inner surface of the lining is evaluated, just as the transient temperature profile in the thermal boundary layer and the emitted enthalpy thereof.