This paper presents the procedure and design principle of heating, cooling and ventilation system on the example of a luxury villa located in the town of Mali Lošinj. The considered object consists of a total of five floors on which there are bedrooms, apartments, living rooms, dining room, reception, fitness, toilets, bathrooms, kitchens, storage rooms and hallways. According to the purpose, the first two floors (basement and high ground floor) are intended for shared use by all accommodation users, while the remaining three floors are exclusively intended for the guest's stay within his accommodation unit. The total floor area of all floors is 1007.4 m2 . Calculations of heat load (according to VDI 2078) and heat losses (according to HRN EN 12831) of individual rooms of the building were performed in order to define the required thermal effects of heating and cooling (calculations have been performed by a computer program „Microsoft Excel“). Observed at the level of the entire facility, the total value of heat losses is 39.5 kW, and the value of heat load is 36.6 kW. A heat calculation was also performed for the needs of dimensioning the DHW system, it is necessary to provide a heat source with a minimum power of 34.9 kW for the system to operate correctly (the calculation was also performed using the computer program „Microsoft Excel“). The building is heated simultaneously by a fan coil and underfloor heating. Underfloor heating plays the role of a basic subsystem in the heating mode, and fan coil units are switched on in case the effect of underfloor heating is not sufficient to maintain the desired temperatures in the premises of the building. For the summer months, the building is cooled exclusively by fan coils. The DHW system is designed and dimensioned in such a way that it is able to provide heating of 1500 l of water to the desired temperature (60 ℃) throughout the year within the estimated time (2 h).