The purpose of this study is to introduce a new methodology for simplifying the degree-hours calculation and to determine the hourly heating and cooling design temperature distribution. Although the concepts of heating and cooling design temperatures are being successfully used in the energy analyses, an hourly heating and cooling design temperature distribution has not been proposed to date. The present model has been developed by using the monthly maximum and minimum outdoor temperatures as parameters in the calculations. The expected average outdoor temperature distribution and the expected design temperature distribution can be estimated by employing the given calculation techniques. Finally, a total of eight cities from Marmara region have been selected to implement the new methodology. We expect this study to be beneficial for designers, engineers and energy managers with respect to building energy analysis.