Hello geo folks I am putting together a water supplied domestic hot water heater from a ex-window a/c of 7500 btu, as a warmup maybe for a whole house heating cooling system. Drilled a 4 -5" well to 100' , hit water at about 22' and marine clay about 2 ft later, stayed in that til about 80' then alternating layers of marine clay and black sand to where i quit at 100'. Put down 3/4" hdpe utube and was going to fill it with the bentonite chips as grout but noticed it stayed full of water at about 20' for a couple days so filled it with sand up to about 10' then sealed it with the chips and ran it about 30' into the house in a 2' trench. I measured the amt of sand going in so i think i got a good continuous fill. Amazing how easily the utube went down in that slick clay once it was full of water and had a couple of old window weights taped on the end! I thought it would be adequate for the 7500 btu water heater but wondered if i could maybe also hook it to a bigger unit for heatin/cooling? So i guess my question is what you can get out of 100' of utube in a sand filled 4-5" hole in marine clay when its flooded about 3/4 of the way?? It occurred to me that it might be way more than the normal 200 ft/ton norm we seem to use here on the non rocky east coast!