In the paper entitled "dimensioning of the heating/cooling system and preparation of the DHW of the Spinut hostel". A special emphasis was placed on the energy renovation of the commercial and residential building, the student dormitory "hostel Spinut" in Split. The work is based on the theory of energy efficiency in buildings, examples of good practice, advice from experts and senior colleagues. The analysis of the current situation defined the actual energy consumption which detected problems with excessive consumption of energy and money through old and energy-poor systems. Total heat losses and gains in calculation part were obtained with the IntegraCAD software package the data obtained that way served as the best evidence of energy obsolete system. The building envelope of the building was renewed using construction measures like insulation of exterior walls and ceiling and the replacement of the existing windows and doors with effective PVC joinery. By centralizing the heating system with the use of RES, replacing the existing heating oil boiler with a heat pump system and installing internal fan coil units. With the mentioned energy renovation measures the concept of low-energy construction has been achieved and considerable savings have been achieved within economic, energetic and environmental aspects. The investment is not negligible but with co-financing and incentives from the EU, it becomes acceptable and profitable for the lifetime of the entire investment.