Cold rolled coils are subjected to the annealing process in order to improve their formability and mechanical properties. A mathematical model of thermal behavior of coils during the heating cycle has been developed. Based on experimental data from several tests, the accuracy of the model has been confirmed. This model enables us to determine the coldest point of coils and the end time of furnace operation. Furthermore, the model has been used to analyze the effect of strip thickness on the heating time required. Thinner strips lead to prolonged heating time and larger temperature differences within the coil.