“ISTEK Chaleur Massique” is used to heat the water for use and also the space in buildings or apartments with a radiator. Where the device will be used, the radiator is removed from its place and “ISTEK Chaleur Massique” is installed in its place. All hot and cold water pipes are connected to “ISTEK Chaleur Massique”. With the radiator system, the space is heated, and also the need for hot water in the apartment is met.