These are several small hot water tanks with heat exchanger located in each unit always with one or more layers of collectors on the roof. It is a distribution of hot water or liquid coolant which in turn heats the water in the water storage tank. This system is used more frequently in the apartment complex, it can be coupled to a heat recovery system on a group of cold production. The heated water is only used to heat water storage tank. This system provides a separate metering of water consumption in homes.