Abstract The estimation of suitable mode of the steel heating is the problem that is also met at annealing of the steel coils. Temperatures inside annealed coil of the steel coils are unknown because it is not possible to measure continually and directly (destruction of the batch, possible defect of the sensor at manipulation with the batch etc.). The missing information about temperature behaviour inside a steel coil can lead to the extension of annealing duration (increasing the energy cost), shortening the annealing duration (poor quality of annealed batch). Presented problems at temperatures estimation in the steel coils help to solve so-called „System of indirect temperature measurement” (SITM). This system is based on direct measurement of the atmosphere temperature in the furnace space between safety cover (bell) and the coil. SITM calculates temperature field inside the coil continually at the time based on continually measurement of the atmosphere temperature TA.