Mr Willy,

Interesting topic. Hopefully you'll get some good input on this from others but I'll throw this out for discussion. My understanding of a geo thermal system is that you use the earth as one big "heat exchanger". You gather heat from it in the winter and use it for cooling purposes in the summer. If I remember correctly, at around 4 feet in depth, the earth remains a relatively constant 51 degrees.

Since your pond could be considered one big thermal mass, I don't see why you couldn't use it as a "heat exchanger" but given your northern location, I would keep the following in mind. For conversation sake, lets say that you will not be using an aeration system in the pond. Holding this to be true, your pond will be subject to temperature differences (at vaious depths) througout the year. In other words, your pond will have a temperature profile. One explanation of this can be found in the publication MANAGING MICHIGAN PONDS FOR SPORT FISHING, Extension bulletin E-1554, page 21.

As shown in the profile, on page 21, during the winter and early spring, pond temperatures below a depth of 10' average between 39-44 degrees. During this time frame, you would want to be drawing as much heat from your geo thermal system as possible. If the temperature of the earth stays at 51 degrees (this you need to verify) and your pond cools to 39-44 degrees, I would think you'd gain more heat benefit from a system buried in earth as opposed to a pond.

Just my thoughts. I welcome all positive and negative responses.

Russ