The objective of this project is to evaluate the energy consumption and the efficiency of glass melting furnaces using a thermodynamic principle and heat (energy) balance analysis. The approach can carry out more accurate result of wall losses than the direct temperature measurement at the furnace walls. Six furnaces from different factories in Thailand were studied. To construct the heat balance of glass furnace, the amount of heat for melting raw materials batch to glass melt (Hex), input energy (Hin) and the heat of content of offgas had to be known. The heat (energy) balance indicated the performance of glass furnaces in term of energy consumption.Glass furnace, Efficiency, Heat balance