Google says the frost line in North Carolina is 12"
It seems like some good insulation around the top 12" of pipe,
the geo-heat might not get let it get too cold.
Looking at the heat transfer, a metal pipe (copper is a good heat conductor),
would allow geo-heat from below the frost line, to be conducted to the surface.
If the pipe is well insulated above the surface and 12" below the surface,
the rate of geo-heat loss
could be very slow,
Maybe allowing the top of the pipe to stay above freezing.
Seems like something you could test this winter.. If it gets real cold.
