To start, I believe I can get away with copper because they use copper to bring city water to the house and it'll last a good 30 + years doing that in Maryland. I can also always add a cathodic low voltage counter action if the ph is too much. Scouring the web, I found this site http://websoilsurvey.nrcs.usda.gov/app/WebSoilSurvey.aspx and it stated that soil ph in my area ranged from 4.5 to 7.3. I have 2.25 acres but would prefer to go in a conical pattern at a vertical angle < 45 degrees at a point that is roughly 25 feet away from the current heat pump location. Using the epa btu calculator, my home requires 58000 btus and 4.9 tons. A little more info is that the house is 3000 square feet, built in the late 50's, has wall insulation and 2 layers of attic insulation, half of the first floor is underground, poured concrete wall. Has anyone done direct exchange? Can you tell me about your setup? Also, I may get chastised for this last question (and I know I'm not the first person to ponder this), but I'd like to at least satisfy my curiosity as to why this is probably a bad idea ... why hasn't anyone tried a dx conversion/retrofit where the coils in a traditional heat pump are replaced with an in ground dx loop? Why would that not improve the efficiency of a heat pump in theory, all else being equal? I do understand that to maximize gains, a purpose built system is best. Thanks for reading.