Large amounts of heat losses occur in pipelines of district heating system. If these lines become insulated, a significant energy savings would be obtained. In this study, by using life cycle cost analysis (LCCA) method, the optimum insulation thickness, energy savings, annual costs and payback period were estimated for various pipe diameters and insulation materials of the heating systems in Isparta/Turkey and in the regions with different degree-day values. As a fuel, natural gas was used in the study. In consequence of the calculations, the optimum insulation thickness was found vary between 0.048 and 0.134m, the energy-saving was found vary between 10.84 and 49.78 $/m; and the payback period was found vary between 0.74 and 1.29 years. According to these results, EPS insulation material with a nominal diameter (DN) of 250 mm provides the highest energy savings, while the lowest value was found to be in fiberglass insulation material with DN 50 mm. As a result, heating systems, selection of suitable pipe diameters and insulation materials with optimum thicknesses provide significant economic advantages and savings. (C) 2013 Elsevier B.V. All rights reserved.