Abstract This paper investigates numerically and experimentally the radiative heat transfer of electric arc furnaces and convective heat transfer of a cooling system for oxygen blowers. The furnaces under study are composed of cooling panels both on the wall and roof, electrodes for creating a magnetic field, a basket containing iron (iron scrap, iron ore & Direct Reduced Iron (DRI)), burners and oxygen/carbon blowers. A 3D model of an electric arc furnace (EAF) with a nominal power of 105 MW and a nominal capacity of 120 T equipped with a cooling box system is simulated using CFD software. A SIMPLE algorithm using the second order discretization method and a DO model of the radiative heat transfer are utilized for simulation of the furnace. The simulation results are validated with the help of thermograph pictures taken from the experimental model. The comparison indicates good accuracy of the proposed model in predicting the experimental results. To identify the reasons for reduced working life of cooling box systems, a number of parameters are studied including the performance of the water cooling box and also the temperature distribution which causes thermal stress. The results of the numerical simulation demonstrate that a poor cooling system in the front panel of the cooling box can degrade its useful life considerably. Meanwhile, a small volume of the cooling water through the devised route and designed arrangement of the cooling box are among the factors which can lead to early failure of this equipment. Taking into account the numerical results and identifying the reasons for the reduced life of the cooling box, a new cooling system for the blower is designed, constructed and tested inside the furnace under real working conditions. The experimental results from one year operation of the furnace show an increased life for the equipment, going from 1500–1775 to 2500 melts. The new model is further developed using the CFD software and the practical results are compared with the new experimental data.