In this master's thesis it is necessary to design underfloor heating system and mechanical ventilation for the building with two swimming pools and additional spaces. The building consists of three floors with total net area of 3800 m2 and it is located in Zagreb. Swimming pool at the ground floor has an area of 400 m2 while swimming pool at basement level has an area of 32 m2. Calculation of thermal losses is determined in accordance with EN 12831. The underfloor heating system is design in order to cover the thermal load due to transmission losses, infiltration and intermittention of the heating system operation. The project heat load is 141 kW while the installed heating capacity of underfloor heating is 90 kW. The rest of thermal load is covered by mechanical ventilation system. The building has three separated ventilation units and eleven suction ventilation system for sanitary knots and showers. One ventilation unit is used for ventilation of the additional spaces while the ventilation system of swimming pool halls is performed separately with two ventilation units. Mechanical ventilation system of additional spaces is design by using hygienic minimum of outdoor air with 35 m3/h per person. Ventilation system for swimming pool halls are design in accordance to the dehumidification requirements. The calculation is determined in accordance with VDI 2089 standard. The hot water system is carried out as a central system with storage tank of 1500 L.