Most residential geothermal heat pump systems use closed-earth heat exchangers constructed of high-density polyethylene tubing. The overall earth heat exchanger usually consists of several parallel piping circuits joined into a set of headers.
In systems using horizontal earth heat exchangers, the header system usually is fabricated in the trench and the entire piping assembly is buried several feet below the surface. Figure 1 (see above) shows an example where six “slinky-” style earth loop circuits have been joined to reverse return headers (seen near the bottom center of the photo).