Abstract This paper reports experimental and Computational Fluid Dynamics (CFD) studies on combustion and radiation heat transfer from a real radiant tube heater. The temperature along the radiant tube as well as at different positions in a test room has been measured. A good agreement between the experimental and predicted results has been found. Based on this validation, the effect of excess air, presented by Air Factor (AF) on efficiency of heater has been studied, theoretically. Moreover, the effect of inlet air preheating on heater efficiency has been examined. The results show that the higher values of excess air can reduce the heater efficiency. The air preheating temperature caused positive effect on heater efficiency. In addition, the results show at higher preheating temperature the effect of AF value on heater efficiency is negligible.