A cogeneration system includes a gas engine generator acting as private power generating equipment for generating power to be supplied to private electricity consuming equipment, and a source-side heat exchanger connected to the gas engine generator through an exhaust heat recovery piping to act as a heat source. A heat medium is heated and evaporated through a heat exchange in the source-side heat exchanger. The resulting vapor is allowed to flow upward to be supplied to room heating heat exchangers. The vapor is liquefied through a heat exchange in the room heating heat exchangers. The resulting liquid is allowed to flow downward back to the source-side heat exchanger. This natural circulation of the heat medium is used for the heating purpose. Surplus exhaust heat is released through a generator to control the heat medium supplied to the room heating heat exchangers. Thus, the private power generating equipment supplies power to the private electricity consuming equipment, while exhaust heat of the generating equipment is used to heat rooms. The entire system is constructed at low cost.
