A downhole heat exchanger, (DHE) also called a borehole heat exchanger, (BHE) is a heat exchanger installed inside a vertical or inclined borehole.[1] It is used to capture or dissipate heat to or from the ground. DHT's are used for geothermal heating, sometimes with the help of a geothermal heat pump. Downhole heat exchangers, like other use of geothermal energy, have the potential to significantly contribute to the reduction of CO2 emissions.[2] In northern Europe, DHE are already widely deployed.[3]