Optimal values for conducting a full-scale plant operation are usually obtained based on experience without the support of theoretical quantitative analyses. In this research, the Grey Relational Analysis method is implemented to develop a model for analyzing the optimal pre-heated air temperature in order to operate a full-scale heating furnace in a refinery plant. Results of using the Grey Relational Analysis as a mathematical method for conducting factor analyses show that the optimal damper angle is 42.5o. This damper angle is close to the actual optimal operational temperature, and if applied, the annual fuel savings will be 1.2 × 106 m3 and 1.4 × 103 ton /year of CO2 emission will be reduced. The Grey Relational analysis is proved to be a suitable model for obtaining valid values of operational parameters concerning the operation of a full-scale heating furnace used in a refinery plant.