64F, yikes. That’s Off for us
We are weenies. Always 70F. 24/7
My Geothermal guy *claims* he has multiple customers with ~3000 sq ft homes that are paying around $500.00 for the entire winter. I forget if he gave me a temperatures. He can monitor the systems remotely so he knows exactly what they used.
Note that most Geothermal homes are newer and ultra insulated.