The paper is a case study of a residential building in a new building, on the site of the city of Poreč, with a theoretical basis that looks at the legislative framework and design parameters of nZEB standards, and deals with the process of designing thermotechnical systems. According to the guidelines for near-zero energy buildings (2019), the choice of thermotechnical systems and energy sources greatly affects the energy performance of a building and meeting the requirements for a near-zero energy building. The same guidelines indicate that eligibility for nZEB buildings can be achieved by different combinations of technical systems and by using different energy sources. Balancing and selection of the optimal thermotechnical system on a residential building in a new building, the paper is made in the program Thorium A + (author of the program: Thorium Software d.o.o.). The analyzed thermotechnical systems (air multisplit system, heat pump and pellet boiler) on the selected residential building meet the nZEB standard, except for the gas boiler, which does not mean that this system is unacceptable in another version and / or in another climate location. In order to make a detailed and comprehensive analysis, additional criteria were taken into account: a) the amount of investment in the thermotechnical system b) energy consumption and environmental and sustainable aspects. The analysis of additional criteria indicates that the thermotechnical system with air / water heat pump is the most acceptable variant for this residential building in a new building.