A couple of years ago we installed a "Water Furnace" with two 300-foot closed-loop vertical wells.
Due to having a log home, we can't really add any significant insulation.
First, let me say, that I am extremely happy with the system we installed. We also figure that we saved about $2400-$2600 the first season, which was far in excess of what we expected (we are into our second season).
We looked at three alternatives for the heat exchanger, and one included one of the ponds. Being where we live, the HVAC people said that when the water is warmest, we need the water cool, and vice versa. We could have done a field, but ... We chose two 300-foot deep closed loop wells that enter the house at 7-feet below ground level. The unlined wells were done in less than a day, which was far cheaper than trying to trench to the pond, or to do trenches for a field.
The system has four separate zones and thermostats which allows us to only only heat/cool the areas we use during that time of day. Our hot water is essentially free. Best of all, the entire system draws very little current when cooling or heating, so when we put in a whole house generator, we only had to put in an 8KW propane system, which is far more than adequate for everything we have -- except the well (it is 600 feet away, and on a separate meter, with a separate small generator). The generator truly runs the entire house, including two refrigerators and a freezer.
