I live in Canada, and in our area we have limited heating source possibilities. Right now we are on electric resistance heat, and it has been reasonable cost, but the utility is proposing doubling the rate over the coming number of years. So Geothermal Ground Source sounds promising. 6000 heating degree days per year in my area. BUT, can it be done? We have an electric forced air furnace, and the ductwork is all behind finished panels. Our yard space is generous (1/2 acre), but still a suburban, not rural, setting. I have a clear 5000 sq foot yard area to heat a 1500 sq foot house, so it might work. And I can take out some trees/bush to expand that a little, if need be. The soil is pure clay, from 6" down to as far as I can dig (some holes to 10'). The one sample I tested (from 5' down) is at just over 25% moisture. Undisturbed soil temperature at 6 1/2' gets down to 36F by April. And only rises to 50F by Sept. Frost can push many feet into the ground, all depends on snow cover and cold snaps. Most 3-ton water-to-air heat pumps are rated to flow 1200 CFM of air, which is what my present furnace with a cooling coil (AC) actually flows. So if I want to retain my existing ductwork, I guess it will need to be a 3-ton unit. And plan to use resistance heat to make up any shortfall, if/when required in a 'hybrid' system. A larger system, with associated ductwork changes, drives the price up far too high. With 36F soil temps in April, if I assume a 15 degree drop, my EWT will be no more than 21F by late in the heating season, and leaving temps running 15F or even less. So I need freeze protection to 10F or so. My present heating load on the 'coldest day of the year' seems to be very close to 150kWhrs (maybe a bit less, at 50 heating degree days), so a 3-ton unit delivering 23,000 BTU (with the low EWT) would be running pretty much 100% of the time under those conditions - but should just keep up, if my calculations and conversions are correct. If I use standard loop sizing for the 3-ton, my soil temps would be dropping quite a bit with the 100 duty cycle, so I expect to use a bit more loop. At least 4 loops of 800' of 3/4" pipe in a slinky arrangement dropped vertically, one each in a 100' trench about 7-8' deep. With a 100' header trench feeding the 4 trenches, also 100' long That trench would be a bit wider. So a total of 500' of trench, 400 with a single slinky loop in each, 100 with 8 single 3/4 pipe, all at the bottom. With the 28% propylene glycol antifreeze I will need, in the above system, it looks like my Reynolds number will be around 1900. I expect to need to use some resistance heat to supplement the geo (and maybe some solar thermal in March/April, but that's another story). Some my main questions are: 1) How much of my present 61 million BTU heating needs per year can the geo supply (heating load for the season is about 18,000 kWhr) vs need for electric resistance heat? 2) how big a problem will the lack of turbulent flow present to achieve the heat flow required for 23,000 btu? 3) how much of an impact will the high duty cycle have on the life of the heat pump? Any help would be greatly appreciated!