When I checked into Geo, I researched both types of systems (closed and open). I was told that a closed system performs worse and worse as the heating season drags on because of the heat loss in the ground around the pipes. They said the ground was a good insulator, and that during cold spells the ground around the coils wouldn't recover quickly. Because I had a pond to dump the water, an open system was recommended vs. a closed system.
What is your usual ground water temp, and can you check the temp of the coolant before it enters the system?
