The optimization of temperature control in a vacuum furnace used for selenization of Cu/In metallic precursors for CIS solar cells is described. The heat transfer between all parts of the furnace was analysed using SIMULINK programming. A system of state equations describing all elements of the object (vacuum furnace) is represented in the matrix form. The performed simulations were compared with experimental variations of temperature with time indicating very good agreement. The results obtained were utilized for the temperature control. A comparison of the constant control signal used in previous experiments with the one obtained from calculations indicates that the desired temperature profile in the furnace is obtained in a much shorter time when applying the calculated control.