This final paper describes the operation of gas VRF systems which instead of electric, have a compressor driven by a gas motor. The calculation and selection of equipment for heating domestic hot water and all toilets with waste heat of a gas VRF engine are presented on the example of the northern building of the University Department of Professional Studies in Split. A comparison was made with the existing technical solution, which is planned in such a way that the domestic hot water is heated by solar collectors on the said building, and the heating of all sanitary facilities with electric heaters. The first part of the paper presents gas engines in general terms, their development through history and significant differences of individual performances. Heat pumps with a gas engine, use of gas in heating and air conditioning are described. The second part of the final work consist calculation of the required amount of domestic hot water for the needs of the entire facility, as well as the selection of associated equipment. The heat load of the sanitary facilities is taken from the existing project of thermotechnical installations (T.D. 870/17) and it is not part of this final work. In third part of the paper, a cost estimate of the existing and designed technical solution is made, as well as an energy analysis to show the cost, and the cost-effectiveness of the designed technical solution in relation to the existing ones.