A method of installing a geothermal heat exchanger (112, 212), the method comprising: at a site, boring a borehole to a borehole target depth in the site; after boring the borehole, inserting a geothermal heat exchanger (112, 212) into the borehole to a desired heat exchanger depth, after inserting the heat exchanger (112, 212) into the borehole, securing the heat exchanger (112, 212) in the borehole at the desired heat exchanger depth; wherein, when the heat exchanger (112, 212) has been secured in the borehole: the heat exchanger (112, 212) has a closed distal end (118, 118A, 118B, 218) and an open proximal end; and the heat exchanger (112, 212) has at least one fluid path between the closed distal end (118, 118A, 118B, 218) and the open proximal end; and installation fluid is disposed in each fluid path of the heat exchanger (112,212); and after securing the heat exchanger (112,212) in the borehole and before excavation of a portion of the site immediatelly surrounding the borehole, temporarily sealing the heat exchanger (112, 212) between the closed distal end (118, 118A, 118B, 218) and the open proximal end by installing, through the open proximal end, at least one respective internal seal (142, 142A, 142B) in each fluid path, wherein for each fluid path, the at least one internal seal (142,142A,142B) is disposed below a respective notional subgrade depth (144A, 144B, 144C); after sealing the heat exchanger (112,212), cutting the heat exchanger (112, 212) above an uppermost one of the at least one seal (142, 142A, 142B) to produce at least one above-seal cut portion of the heat exchanger (112, 212); after cutting the heat exchanger (112, 212), removing each above-seal cut portion of the heat exchanger (112,212) 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 (144A, 144B, 144C); and after excavating the portion of the site immediately surrounding the borehole, removing the seals (142, 142A, 142B) for connection of the heat exchanger (112, 212) to supply/return conduits. at a site, boring a borehole to a borehole target depth in the site; after boring the borehole, inserting a geothermal heat exchanger (112, 212) into the borehole to a desired heat exchanger depth, after inserting the heat exchanger (112, 212) into the borehole, securing the heat exchanger (112, 212) in the borehole at the desired heat exchanger depth; wherein, when the heat exchanger (112, 212) has been secured in the borehole: the heat exchanger (112, 212) has a closed distal end (118, 118A, 118B, 218) and an open proximal end; and the heat exchanger (112, 212) has at least one fluid path between the closed distal end (118, 118A, 118B, 218) and the open proximal end; the heat exchanger (112, 212) has a closed distal end (118, 118A, 118B, 218) and an open proximal end; and the heat exchanger (112, 212) has at least one fluid path between the closed distal end (118, 118A, 118B, 218) and the open proximal end; and installation fluid is disposed in each fluid path of the heat exchanger (112,212); and after securing the heat exchanger (112,212) in the borehole and before excavation of a portion of the site immediatelly surrounding the borehole, temporarily sealing the heat exchanger (112, 212) between the closed distal end (118, 118A, 118B, 218) and the open proximal end by installing, through the open proximal end, at least one respective internal seal (142, 142A, 142B) in each fluid path, wherein for each fluid path, the at least one internal seal (142,142A,142B) is disposed below a respective notional subgrade depth (144A, 144B, 144C); after sealing the heat exchanger (112,212), cutting the heat exchanger (112, 212) above an uppermost one of the at least one seal (142, 142A, 142B) to produce at least one above-seal cut portion of the heat exchanger (112, 212); after cutting the heat exchanger (112, 212), removing each above-seal cut portion of the heat exchanger (112,212) 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 (144A, 144B, 144C); and after excavating the portion of the site immediately surrounding the borehole, removing the seals (142, 142A, 142B) for connection of the heat exchanger (112, 212) to supply/return conduits.