The diploma thesis analyzes the consumption of energy for an existing building. The analysis is based on measurements of electricity and heat consumption. By using the measured data base temperature, energy signature and performance line, are determined. These data and heating degree days are used to analyze the consumption of energy for an existing building. The purpose of the analysis is to try to evaluate thermal-technical properties of the building and to try to assess the accuracy of the results according to the monthly energy consumption data for the existing building.