A heat balance is usually carried out to determine the energy inflow and outflow for a thermal system and thus determine the overall system performance. The heat balance for a gas-fired furnace for melting non-ferrous metals has been determined. 50 kg of Aluminium charge was melted in the furnace and the in-furnace, walls, roof and exhaust gas temperatures were measured. Experimental measurements taken from the furnace operation were fed as input to a MATLAB program which was developed based on heat balance equations. The output from the program show that about 10% of the heat energy is lost through the walls and roof while 64% is lost through the exhaust gas. The thermal efficiency and melting efficiency determined for the furnace are 36.39 and 54.6%, respectively. The low energy loss through the walls and roof is due to use of appropriate wall thickness. The highest energy loss is through the exhaust, hence, the incorporation of a recuperator to make use of exhaust gas waste heat to preheat the combustion air or the metal charge or both, will further enhance furnace efficiency.