Downhole heat exchangers have been used extensively in Turkey from 1981 to 1990. One of these installations is part of the geothermal district heating system in the city of Balçova near Izmir on the west coast of Turkey. These downhole heat exchangers are some of the largest in the world in terms of energy output. During the period 1981 to 1997, there were 11 DHE installations in Turkey, but now there are only five - two in Simav and three in Balçova