Heating degree day is an essential parameter for estimation of energy demand and consumption in buildings. In the case of hourly temperature data availability, it is more appropriate to use the hourly method to calculate heating degree days. In the situation of reduced meteorological data, other methodologies must be selected for calculation. These methodologies include ASHRAE and UKMO methods. The aim of the present study is to analyse the effect of substitution in the heating degree day calculation method to modify building recommendations of current Chilean thermal building codes, maintaining the transmission heat losses through thermal envelope of buildings, in various geographical locations, with different climatic conditions. Analysing the data obtained from 165 meteorological stations, it has been discovered that there are significant differences in the geographical distribution of heating degree days calculated with ASHRAE and UKMO methods in desert areas, while heating degree days are similar in regions with a more temperate climate with both methods. When there is a significant frequency of days with large daily temperature amplitude, it is more advisable to use the UKMO method for the calculation of heating degree days. For all these reasons, new values of thermal transmittances have been proposed for the opaque elements of the thermal envelopes with the developed methodology. A reduction by up 65% of the values of thermal transmittances are required using UKMO method in desert areas and no variations are required in cold zones. The new values of thermal transmittances proposed will help to improve the energy performance of buildings and to achieve a better adaptation to the climatic conditions.