The STHAL network was created in 1969 to supply the northern quarters of Melun. At the time, using geothermal energy to power a heating network was a totally original idea. In fact, it was the first time geothermal energy had been used to power a heating network in France. Melun uses the same geothermal source for heating and for domestic hot water, which are supplied over separate networks. This system makes Melun a unique network, and it supplies 4,000 housing units and 2,000 equivalent housing units of public buildings. In most cases, heating and hot water are supplied over a common network and are separated at substations located outside the buildings they serve.