In this final paper is presented the reconstruction of an existing family house, the achievement of the status of an nearly zero energy building (nZEB). The first part of the paper shows in general which buildings are almost zero energy, which criteria must be met and why new buildings are built as nZEB. It also describes which technologies are used for the heating and cooling, and production of electricity and hot water. The next chapter presents the work in the computer program Ki Expert Plus and the comparison of the building components of the existing and nZEB building. Based on the calculation of the required thermal energy for heating and cooling, the program prepares an energy certificate which is presented in this paper work and which shows the energy class of the building. The fourth chapter shows the calculation of heat load or total heat loss of heated rooms. In accordance with the total heat losses, in the fifth chapter are selected the powers of the radiator and the pellet boiler that make up the thermotechnical system. The boiler, piping and radiators are plotted on the ground floor plan and show their exact positions.