Ground-source or geothermal heat pumps (GHPs) are attractive alternative to conventional heating and cooling systems owing to their higher energy utilization efficiency. In this regard, GHPs have had the largest growth since 1995, almost 59% or 9.7 annually in the United States and Europe. The installed capacity is 6,850 MWt and annual energy use is 23,214 TJ/yr in 26 countries. The actual number of installed units is around 500,000. The utilization of GHPs in residential buildings is new in Turkey, although they have been in use for years in developed countries. In other words, GHPs have been put on the Turkish market for about three years. There are no Turkish GHPs’ manufacturers yet