According to PrecisionMachinisT :

"Chris Lewis" wrote in message
...

There's another factor to consider - the geothermal will shut down
even if it's above the threshold if it figures the ground loop has made
itself too low. So an undersized unit may "freeze out" it's heat
exchange branches during sustained low temperatures, and effectively
not work at all.

And with many properly installed / sized geo units operating with a COP of 4
or better these days, then if / when the system defaults fully to the backup
heat strips then it's well to remember its gonna cost you 4 times as much to
run at capacity.

If it's at all capable of doing so. We had a geothermal company out,
and they were spec'ing it with a mere 5Kw of backup heat. Which if the geo
primary goes out, you're going to freeze.

[We could only get away with that because we have _baseboard_ heat, and
we weren't planning on tearing it out.]
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.