Here in the NW most homes are or were heated by oil. The biggest cost of switching to gas (as geothermal is very expensive) is decommissioning the old buried oil tank, in many cases up to 675 gal. cap. I was pondering weather the old tank could be filled with a solution and somehow figure out how to get piping into the tank without digging it up and using it as a fluid to fluid heat exchanger for HVAC. Anyone wanna run with that ball?