Been wanting a geothermal heatpump for a few years and finally see the light so I''m getting down to more design questions. I have two wells on my 1.2 acres. One's an old brick hand dug ground water well that's 36 feet deep and 30" in diameter. At rest it's got about 30 feet of water in it. I'm in the process of revitalizing it by keeping the water level down about 20' or so. Between it and my other well, a much deeper traditional 8" well that hits a different water table much further down (don't know how deep but it's got a lot of sulfur that this old ground water well doesn't. Anyway, if the deeper well can pump at least 5-10 gpm I know I can go open loop but was wondering if it would work to put a slinky closed loop down into the 30" well and let it take the heat/cool directly from the water. What I don't know is would there be enough water in it to act much like a pond. I figure I could hook up a thermostat controlled pump that would pump out some water if it got too warm or too cold... What I don't know is how much heat would be transferred into or out of the well through the bricks. Would it be enough to keep the water temp stable enough to support a closed loop? Is there a formula for computing such a thing. I PS: I'm in southern Michigan so it gets pretty warm.. in the summer and cold.. but not MN cold in the winter. I'm thinking about 3 - 3.5 Tons would do the job for my 1892 farmhouse... 1850 sq feet.. with double pane windows and good attic insulation and insulated fiberglass siding. PS: In really cold times, I have 170k BTU worth of coal stoker stoves and a propane FA system. Any input on the best way to approach these wells and whether you think my closed loop idea might work would be appreciated.