The reduction, of energy cost related to the oil final product, related to energy efficiency is gaining importance day by day. Oil refineries are high energy consuming systems. Furnaces used in various parts of refineries are the main cause of this consumption. The flue gas oxygen level can be reduced by replacing old type burner with ensuring better combustion in furnaces. In this study, the effect of energy efficiency was investigated for replacing burner in a furnace that supplies heat to reboiler side. The flue gas oxygen values were measured during operating conditions and after application in the furnace burners. According to the results, while the flue gas oxygen value before application of the burner replacement is 5%, it can be reduced to 2,1%. Thus, the efficiency of the furnace has increased from the 88.7% to 90.08%.