The work presented in this report investigates the effect of replacing natural gas fuel in a radiant tube burner in an industrial furnace with hydrogen fuel. The flue gas is fully contained inside the radiant tube burner and does not come into contact with the iron products inside the furnace. The burner interacts with the process side of the furnace only by heat transfer. Therefore, the investigation could be divided into a study of two separate systems: the burner and the furnace systems. In the first part, the burner system was evaluated. The impact of changing the fuel of the burners from natural gas to hydrogen on heat-, flow- and radiation of the existing burner was studied. Moreover, the NOx generation has been considered. The investigations were performed using Reynolds Average Navier Stokes (RANS), Computational Fluid Dynamics (CFD) approach using detailed chemistry. Natural gas combustion was simulated as the basis for comparison. The result shows that the CFD model could estimate the NOx emission of the base case well. Next, the combustion with hydrogen was compared. The result suggests that the thermal efficiency of the burner is slightly higher with hydrogen fuel. On the other hand, the NOx emission is significantly higher. A modified burner including internal flue gas recycle was proposed and studied. The result shows that the modified burner can be operated at the same power and the same level of NOx emission as the existing system. Furthermore, different burner power could be applied in order to comply with the NOx emission limit or to increase processing speed. In the second part, a heat transfer analysis of the furnace has been performed. The model agrees well with measured data of furnace atmosphere temperature. The result suggests that having a higher burner power could increase the processing speed and reduce the energy requirement per ton of iron products.