Recently, the production of electrical and thermal energy is starting to be a challenge for most modern states. Harmful ecological impacts of the energy sector are inevitable and the changes are necessary. Along with the energy refurbishment of existing building we achieve the reduction of the energy required for a comfortable stay in the buildings, reducing environmental pollution, reducing the annual energy costs, thus making life easier. This project follows the standardized methods of calculating the energy required in one year. The recordings and measurements of the observed building, which includes collecting and processing data on the state of the object, is necessary in order to obtain the necessary data for determining the thermal conductivity of the individual layers, the heat transfer of each building part as the essential characteristic of the external element in the analysis of total heat losses, and thus the necessary thermal energy for conditioning the building. The first part of the project shows the current energy sector and the concept of energy refurbishment of the building, the description of the observed building and the technical systems in it to get the first insight into the characteristics of the building from the energetic standpoint. The second part of the project includes the procedure for calculation of the required annual thermal energy for the building in accordance with the valid Algorithm for calculating the required energy for heating and cooling according to HRN EN 13790, results for the observed building calculated using the computer program Ki Expert Plus which is using the above-mentioned Algorithm developed according to HRN EN 13790 and determining the energy certificate. The third part of the project contains an analysis and suggestion of measures to improve energy efficiency, selection of the most favorable measures and energy certification after their implementation