The paper analyzes energy auditing and energy certification, as well as the analysis of suggested measures of saving on the example of a residential building. The paper analyzes the properties of heating, cooling and consumable hot water systems. After analysis of the current situation, the calculation of the required heat energy for heating and cooling is described. The KI Expert plus computer program was used to calculate the reference annual heat and cooling energy for heating and cooling. Based on the results; construction, electrical and mechanical engineering measures are proposed to improve energy efficiency. The cost of the investment, the estimated energy savings and the estimated savings in HRK/yr, the unique return on investment and the reduction of CO2 emissions are calculated after all the proposed mechanical energy efficiency measures. The paper analyzes two variants of mechanical measures of a heat source to replace a wood boiler. As a new source of heat, the heat pump and the pyrolysis boiler were analyzed. Analyzing the installation of a gas heat pump would save more energy, increase the estimate of financial savings, and the simple payback period is shorter. While the pyrolysis boiler has a greater reduction in CO2 emissions.