He was getting nothing free at all. It was a heat pump, and as McCloud explained it is the same as a fridge. they even use fridge compressors. Is "moves" heat from the earth into the house, as a fridge moves heat from the cabinet into the condensing tubes at the back of the fridge.
The compressor costs to run. The running costs of a ground sourced heat pump is about the same as natural gas. He has a trench (surface) ground heat pump system. The best are where you have a bore hole 50 to 60 foot deep. Surface systems can run out of available heat giving only low grade heat, not enough for hot DHW.
That church would cost a lot of money to heat as insulation was not a major part of the construction. I would have pulled the church down and built a proper eco house. The old stones could have been used to clad, or add thermal mass to a new eco house, still giving a link with the past.