In an industrial building, several refuse hot-air flows (RHAF) are often available. We use a recovery heat exchanger (RHE) to heat incoming air for space heating by using a mixture of these RHAFs. A proper scenario for use of their heat contents is essential for efficient control of the energy system to achieve the greatest energy-saving efficiency. Software has been used in an industrial building with three RHAFs to control their mixtures. Depending on the temperatures of the colder and hotter zones of the industrial building and the outside temperature, we can find regions for use of RHAF mixtures of particular compositions and avoid energy losses while maintaining good thermal comfort in the building.