[gorush]

Our home is heated and cooled by a closed-loop geothermal system. The system works great until the temp drops substantially below zero F. The home is earth sheltered with ICF construction so heat loss is less of an issue than most.

[69ConvertibleFirebird]

The system works great until the temp drops substantially below zero F.

Why would that be since you are extracting heat from in-ground water at roughly 55 degrees, year-round? I would think that the efficiency would be consistent no matter what the air temperature (since it doesn't use outdoor air as the heat exchange medium). I obviously don't understand something about geothermal.

[Eric in the Ozarks]

We built new in ‘02 and included a ground source heat pump with four 200 foot wells under the driveway. The Water Furnace unit inside the house has a noisy scroll compressor, otherwise it works great. We've had no service calls.
The WF also heats the floor in the main level with forced air upstairs. I can adjust the forced air duct to put some heated air downstairs but this is rarely needed.
Our house is built into the side of a hill with an insulated wall and floor. We sealed all the receptacles and double house-wrapped the corners. Blown cellulose in the walls and ceiling, plus the best Andersen windows I could buy complete this package.
Power bills are +/- $100/month.
Needless to say, I'm sold on geothermal.

[mountn man]

I've been interested in ICFs and geotherm for awhile, and want to build in the next 2-3 years.

Is your whole house ICF? How are your heating bills.