A method of installing a geothermal heat exchanger , the method comprising: at a site , boring a borehole to a borehole target depth (D) in the site ; after boring the borehole , inserting a geothermal heat exchanger into the borehole to a desired heat exchanger depth, after inserting the heat exchanger into the borehole , securing the heat exchanger in the borehole at the desired heat exchanger depth; wherein, when the heat exchanger has been secured in the borehole : the heat exchanger has a closed distal end and an open proximal end ; and the heat exchanger has at least one fluid path between the closed distal end and the open proximal end ; and installation fluid is disposed in each fluid path of the heat exchanger ; and after securing the heat exchanger in the borehole and before excavation of a portion of the site immediatelly surrounding the borehole , temporarily sealing the heat exchanger between the closed distal end and the open proximal end by installing, through the open proximal end , at least one respective internal seal in each fluid path, wherein for each fluid path, the at least one internal seal is disposed below a respective notional subgrade depth ; after sealing the heat exchanger , cutting the heat exchanger above an uppermost one of the at least one seal to produce at least one above-seal cut portion of the heat exchanger ; after cutting the heat exchanger , removing each above-seal cut portion of the heat exchanger and excavating a portion of the site immediately surrounding the borehole ; wherein excavating the portion of the site immediately surrounding the borehole is above a lowermost of notional subgrade depths ; and after excavating the portion of the site immediately surrounding the borehole , removing the seals for connection of the heat exchanger to supply/return conduits . at a site , boring a borehole to a borehole target depth (D) in the site ; after boring the borehole , inserting a geothermal heat exchanger into the borehole to a desired heat exchanger depth, after inserting the heat exchanger into the borehole , securing the heat exchanger in the borehole at the desired heat exchanger depth; wherein, when the heat exchanger has been secured in the borehole : the heat exchanger has a closed distal end and an open proximal end ; and the heat exchanger has at least one fluid path between the closed distal end and the open proximal end ; the heat exchanger has a closed distal end and an open proximal end ; and the heat exchanger has at least one fluid path between the closed distal end and the open proximal end ; and installation fluid is disposed in each fluid path of the heat exchanger ; and after securing the heat exchanger in the borehole and before excavation of a portion of the site immediatelly surrounding the borehole , temporarily sealing the heat exchanger between the closed distal end and the open proximal end by installing, through the open proximal end , at least one respective internal seal in each fluid path, wherein for each fluid path, the at least one internal seal is disposed below a respective notional subgrade depth ; after sealing the heat exchanger , cutting the heat exchanger above an uppermost one of the at least one seal to produce at least one above-seal cut portion of the heat exchanger ; after cutting the heat exchanger , removing each above-seal cut portion of the heat exchanger and excavating a portion of the site immediately surrounding the borehole ; wherein excavating the portion of the site immediately surrounding the borehole is above a lowermost of notional subgrade depths ; and after excavating the portion of the site immediately surrounding the borehole , removing the seals for connection of the heat exchanger to supply/return conduits . <EOS>