This project involves a complete overhaul of the heating system and domestic hot water preparation in the industrial production building within the INA Oil Refinery in Sisak. The goal was to modernize the existing system by replacing old gas boilers with new, more energy-efficient installations. The project implemented a gas absorption heat pump and condensing heaters, significantly improving energy efficiency, reducing costs and CO2 emissions, and ensuring reliable heating and thermal comfort. This project not only enhanced energy performance but also served as an example of sustainable business practices, reducing the environmental footprint and promoting the use of green energy.