A ground source heat exchanger for use with a heat pump. The heat exchanger comprises a foldable, expandable outer pipe with an inner pipe that is placed within a borehole. The outer pipe may be folded and sealed at one end while out of the borehole. The outer pipe is inserted into the borehole then expanded by pressure to minimize the annulus between the outer pipe and the ground. The inner pipe is inserted and the inner and outer pipes are connected to the heat pump for circulation of heat exchange fluid.