is anyone here familiar with an architecture in Europe referred to as Passvhaus where the primary Heating source is referred to as the construction material , then geothermal heatpump and usually combined with solar, Very well insualted home and some incite to components as well to retain heat. I have one place with it a house where the geothermal feeds underfloor manifolds for each zone , I have been there when down in the 40sf outside and people inside none the wiser heat is made in cylinder but not even being used yet, which is almost unheard of in normal house construction. obviously high first cost investment, but rapid payback in energy savings , this system also makes the DHW.
Keep it simple to keep it cool!