I have a 30 year house that currently has oil heat and no air conditioner. I'm considering going to a Geothermal HVAC system.

My 2-story house is 1400 square feet, not including the basement. I live on 5 acres in Southeast Michigan. My water table is about 7 feet below the surface.

My wife wants a pond in the low-lying area in my front yard, so I'm thinking I can combine her pond with a Geothermal system.

Two rooms have ducts that run on the outside of the house. I've been told that Geothermal systems need special insulated ducts.

My attic has 2 ft of blown insulation, but the walls feel cold in the winter. The walls are 4 inches thick with fiberglass insulation, but there is no Tyvak and no styrofoam insulation sheets below my aluminum siding. I think I'm getting air infiltration.

Is it reasonable to explore a Geothermal HVAC system with a house such as mine? Or is Geothermal more for a new house that's designed for Geo?

Any recommendations of a particular brand?

Thanks in advance for any advice!