A method for manufacturing U-shaped downhole heat exchangers that are directly connectable, as an evaporator, to a heat pump, with the following method steps: a) two PE coated copper pipes (2, 3) of a suitable predetermined installation length are synchronously rolled up onto a drum, b) the two free ends of the PE-coated copper pipes (2, 3) are stripped, so that two uncoated, stripped copper pipe end sections (2a, 3a) are formed, c) a piece of heat-shrink tubing (4 or 4a and 4b) is slid either onto one end or onto each one of the ends of the copper pipes (2, 3) in such a manner that the stripped end sections (2a, 3a) of the copper pipes remain uncovered, d) a separately manufactured U-shaped pipe section made of copper is slid onto the two uncoated copper pipe end sections (2a, 3a), fixed thereto and connected in a pressure-tight manner with the copper pipe end sections (2a, 3a), e) the piece of heat-shrink tubing or the pieces of heat-shrink tubing (4a, 4b) are then pushed back until the U-shaped pipe section, the provided PE-coating and the junctions between the U-shaped pipe section and the ends of the copper pipes (2, 3) are completely covered by the pieces of heat-shrink tubing (4 or 4a and 4b), f) the slid-on pieces of heat-shrink tubing (4a, 4b) or the piece of heat-shrink tubing are then heated and shrunk, g) a pre-fabricated plastic cap made of a shrinkable material is then slid onto the U-shaped pipe probe section until the junctions are covered and shrunk by heating, h) the interior space of the plastic cap is filled with a castable plastic material as a casting compound and i) after curing, the remaining end of the copper pipes (2, 3) of the completed downhole heat exchanger is rolled up again onto the drum. a) two PE coated copper pipes (2, 3) of a suitable predetermined installation length are synchronously rolled up onto a drum, b) the two free ends of the PE-coated copper pipes (2, 3) are stripped, so that two uncoated, stripped copper pipe end sections (2a, 3a) are formed, c) a piece of heat-shrink tubing (4 or 4a and 4b) is slid either onto one end or onto each one of the ends of the copper pipes (2, 3) in such a manner that the stripped end sections (2a, 3a) of the copper pipes remain uncovered, d) a separately manufactured U-shaped pipe section made of copper is slid onto the two uncoated copper pipe end sections (2a, 3a), fixed thereto and connected in a pressure-tight manner with the copper pipe end sections (2a, 3a), e) the piece of heat-shrink tubing or the pieces of heat-shrink tubing (4a, 4b) are then pushed back until the U-shaped pipe section, the provided PE-coating and the junctions between the U-shaped pipe section and the ends of the copper pipes (2, 3) are completely covered by the pieces of heat-shrink tubing (4 or 4a and 4b), f) the slid-on pieces of heat-shrink tubing (4a, 4b) or the piece of heat-shrink tubing are then heated and shrunk, g) a pre-fabricated plastic cap made of a shrinkable material is then slid onto the U-shaped pipe probe section until the junctions are covered and shrunk by heating, h) the interior space of the plastic cap is filled with a castable plastic material as a casting compound and i) after curing, the remaining end of the copper pipes (2, 3) of the completed downhole heat exchanger is rolled up again onto the drum.