Pete,
Sri bout the delay in responding but just returning from playing with the buffalo on the dakota plains.
Think a moment about the concept and efficiency of a geothermal system. You are attempting to normalize your thermal point of contact to be nearly the same temp year round. This minimizes the amount of energy required to set your house at a living heating/cooling temp. The farther north you go (but below the artic circle) you will find a termal mass which is about 55 or so degrees year round. If your water exchanger is forced to work from a base of thirty something degrees you have a gain over sub zero air to air systems but still requires a lot of energy to get up to seventy something. Your northern climate may not be the best place to think water.
