Waterfurnace Thermostat Wiring Diagram - How to tell if your system is Nest thermostat compatible and get a wiring diagram. The Nest app now includes steps to check thermostat compatibility and give you a custom wiring diagram. Geothermal heating is a pretty cool technology. It saves a lot of money in heating and is much more efficient than fuel oil or propane. There are many web sites explaining the technology so I will not spend too much time with that.. I purchased a GEO Cool system 5 ton with a 2 stage pump for my new house construction with the intention of doing a DIY. I have a large excavator so laying the piping is a piece of cake, but the system did not come with *ANY* instructions on how to do the internal connections..