Abstract. The iron and steel industry is one of the major industries for developing countries, and it is ranked as one of the industrial sectors that have the highest energy consumption. It is also served as a primary industry that provides materials to secondary industries as well. This present study focuses on a slab, a product from a steelmaking process, which will be sent to a hot-rolling mill to form a final product. Before the rolling process, slab is heated to a proper temperature by charging into a reheating furnace. Heat is generated by a combustion process from direct-fired burners. In general, heat loss from the reheating furnace occurs by several mechanisms including the flue gas loss. Although a recuperator is used to reduce heat loss by recovering some of that to preheat the combustion air, the exit flue gas temperature is still as high as 350-450C. This research paper aims for the investigation of the energy efficiency resulted from the implementation of a slab preheating chamber before charging into a reheating furnace. Four different sizes of the preheating chamber are selected as the case studies for the energy analysis. Another consideration includes the acid dew point of the flue gas as the lowest criteria for the flue gas temperature. The result indicates that the flue gas temperatures are above the acid dew point for all four cases under consideration. The slab temperatures increase from the ambient temperature of 30 o C to 59.52 o C, 75.98 o C, 84.98 o C and 89.46 o C, respectively, before begin charged into the reheating furnace. As a result, the fuel energy consumption after the implementation of the reheating chamber is reduced by 0.94%, 1.46%, 1.75% and 1.89%, respectively comparing to the furnace without the reheating chamber. The reheating furnace efficiency also increases from 69.88% to 70.54%, 70.92%, 71.13% and 71.22%, respectively.