For a family house near the city of Varaždin a project for heating, cooling and hot water preparation was carried out. The family house consists of nine rooms of which eight are heated. It is prefabricated house and has a exterior wall thickness of 0.306 m and the thickness of the inner walls of 0.16 m. The project was carried out in the form of the main mechanical project with all the accompanying elements (budget, drafts, choice of the system equipment and the system costs). The complete calculation of heat losses, thermal gains and heat transfer coefficient was performed in IntegraCAD. The heating, cooling and hot water preparation system was performed with the air – water heat pump. The floor heating system was performed throughtout the house except in the hallway and pantry. The cooling system was designed in such a way that fan-coils were installed in two rooms (kitchen with dining-room and living room). In case of heat pump malfunction, an electric water heater was installed as a safety system to ensure that the system can continue to work. The equipment system and the system costs were selected by the results of the evaluation. Finally, the energy certificate was calculated in the KI Expert plus program.