OK I have to throw out another one.
There was a discussion about this years ago, but I have to admit the current posters appear a lot more knowledgeble.

I just read a case study, where the ground loop was placed under the home.  It was in Colorado, zone 5 a 3100 sq ft ranch home. Insulated to approx current code minimums, plus r 10 underslab.  It had a basement, so they over excavated 5 additional feet, leaving the loop 12 feet below finished grade. 

They claim it is very successful.  Now I realize this is not often done but am wondering why. If the loop is a full 5 feet below the slab would it have any affect? Would frost heaving be an issue at that depth?  If you were insulating to r18 to 20 under the slab I would not think there would be much affect there. (the study claims ave slab temps at 68 degrees.

The obvious advantage would be cost savings in excavation, and having to dig up less of the site. 

An obvious disadvantage would be there is no access to the loop afterwards if it failed, but really if it did, would you just not install a new one instead of patching the old?   There would probably be some compaction required before installing footers,  but that would seem to be advantageous to the loop as well.


I have seen Vertical bore under the home but not horizontal.

In a slab on grade that would put the loop 6 to 7 feet below grade, with a nice warm house 5 feet above.

What say you Geo wizards?

A concern I would have would be of getting that 5' of backfill between the geothermal loop and the basement slab/footings sufficiently compacted so as to not have settling issues down the road. Another concern up north in the winter would be the loop pipes freezing the ground beneath basement slab/footings. Even localized freezing around the pipes could lift the slab and cause cracking.

There is usually not any where close to enough area under the slab for the amount of pipe required.

I would agree with what geodean and arkie6 wrote and add that this just does not make good sense

It's not clear to me that digging at the bottom of a basement + compacting is a cost savings over digging elsewhere.

Posted By jonr on 02 Oct 2012 12:46 PM
It's not clear to me that digging at the bottom of a basement + compacting is a cost savings over digging elsewhere.

I was thinking the same thing here also. In terms of cubic feet of earth moved in order to bury a heat exchanger. This has got to be the hardest way to do it.

I a 40 X 50 ranch was to employ say a 3 ton geo it would require in my AO 3, 3' trenches 110' long on 12 foot centers some variation of that sized foot print. So as Dewayne said I don't know how you'd fit horizontals under a typical home.
DX systems have a loop design that is about 500SF/ton, but you will most surely freeze soil. Is that okay?

Do you have a link to the case study?


Instead of loops in that area, (12' deep trench in a Ranch? Not me in that hole) maybe, how about:

Hot Rocks Thermal Energy Store

2nd Level Basement

Buried Buffer Tank

Fallout Shelter (why don't we have more of these anymore?)

Root Cellar

Here is a link to the case study:

http://pkgeothermal.com/Case_study-3100_sq_ft_home.pdf