The main objective of this manuscript is an analysis and a particular review of the heating degree-days for a long time period (1925-2018) in the big-sized cities. In this regard, daily air temperatures outside are important with stress on hourly and half-hourly values of air temperature which should facilitate the- determination of heating demands for different type of buildings. Multifarious criteria for calculating degree-days of heating and their comparison have been clarified. Different countries with different threshold temperature parameters for buildings of multifarious purposes were enumerated. There is noticeable decreasing of the values of heating degree-days in the big-sized cities, which is the result of climate changes. This is essential for intermittent heating of the households and office buildings, which is the instrument to prevent squander of energy. The regulation of threshold temperature with the aspect of thermal comfort of inhabitants has been considered, too. All of the paper´s hypothesis were elaborated on the territory of the Serbia´s capital city Belgrade.