My last house had a very early total loss geothermal system from the 1983? Pumped from our well, dumped into the sewer. It was still working as of 2013 when my dad removed it for a newer much more efficient system. That said, our heating bills for an 1800sqft 1960 house was always under $200, kept it at 66 degrees. The heater vents saw air about 105 degrees F with JUST the geothermal, and 115 with the electric coils on.
The newer variable pump systems are crazy efficient, my dad saw almost a 50% reduction in month-to-month cost, and his air outlet temp is over 110 with just the geothermal, no electric. Also, recirculates the waste through the hot water tank so that almost never comes on.
Geothermal is where it's at. I could go on and on haha.
Oops my bad, our house was ALL electric, so those bills are for everything. Not sure if you have any gas.