Energy consumptions in buildings can be reduced considerably using insulation materials. Even in well-insulated buildings energy consumption can be reduced further by insulating transmission pipes. For this reason, the energy savings can be obtained by using proper thickness of insulation in these areas. In this study, insulation thickness has been optimized by using exergy method and life-cycle cost concept for the case of using various fuels such as coal, natural gas and fuel-oil. This analysis is based on the exergetic cost of insulation materials and fuel. As a result, combustion parameters such as excess air, stack gas temperature, and combustion chamber parameters are much more effective on optimum insulation thickness. The optimum insulation thickness decreases with the increasing of inlet temperature of fuel, and with the decreasing of excess air coefficient, temperatures of stack gases and combustion chamber. Under this effects, the optimum insulation thicknesses determine as 0.065, 0.071, 0.099 m with a rate of 68.27%, 71.54% and 77.85% in the exergetic saving for natural gas, coal and fuel-oil fuels, respectively. The optimum insulation thickness, total annual exergetic cost, exergy saving, and exergy losses depending on heat transfer increase with the increase of heating degree-days, while they decrease by increasing the temperature of outside air (reference state). In addition, the optimum insulation thickness for the exergoeconomic optimization is higher than that of energoeconomic optimization. (C) 2012 Elsevier Ltd. All rights reserved.