Insulating is the most effective method coming, that is used to gain energy in buildings. In this work, the analysis of optimum insulating thickness in heating and cooling, by using different fuels (natural gas, coal, fuel-oil and electric) and types of insulation (XPS and EPS), total cost, repaying span, saving energy, and environmental was made. By fixing of average optimum point belonging to İzmir, Bursa, Konya and Erzurum; insulating thickness is respectively, 0.065 m, 0.083 m, 0.099 m and 0.126 m, in heating and 0.028 m, 0.016 m, 0.013 m and 0.006 m in cooling The annual earnings, occurred in heating respectively, 20.53 $/m2, 32.85 $/m2, 49.92 $/m2 and 75.64 $/m2, while in cooling 3.76 $/m2, 1.19 $/m2, 0.77 $/m2 and 0.24 $/m2. The repaying span took the value of; in heating respectively 1.67 years, 1.52 years, 1.42 years and 1.32 years, while in cooling 2.70 years, 4.6 years, 5.88 years and 12.48 years. CO2 and SO2 emissions released to the environment have been observed to decrease by about 81 % at the optimum point compared to the uninsulated state, and a significant amount of benefit has been achieved.