I live in a 5 year old log home with a detached 3 car garage and 800 sq. ft. apartment above it in Connecticut. My home is roughly 3000 sq. ft. including finished basement and is 100% radiant heat, the garage is also radiant and the apartment is baseboard. All the heat and domestic hot water for the house (garage and apartment have electric water heater) is handled by a 100K BTU buderous oil fired boiler. This is where I'm trying to be creative, I have a drilled well that services the house (380 ft deep) and as luck may have it, the driller hit an aquifer that overflows 8 gal/min out the cover of my well. We have since cut a hole in the well casing 2-3ft below the surface and ran an overflow pipe into the woods and it now fills a pond I dug. Would it be worthwile to run a pipe from the well overflow into my basement and connect it to a heat exchanger to either help heat my radiant in the winter, or run cool water through it in the summer (to help out the central AC). I know very little about geothermal, but recently struck up a conversation about it with someone and this idea came to mind. I did some searching online, but haven't found a whole lot of info. Any feedback would be much appreciated. Thanks a lot.

Heat transfer is always driven by temperature differences , What temperature can you expect summer & winter from the well water?

You need at least 15 degrees F hotter than the receiving stream to have an effective water to water heat exchanger of reasonable size & cost. If you are heating air the difference must be a lot higher . Think of old cast iron radiator heating. The most common way of heating with well water is via a heat pump ( reverse operation air conditioner ). The capital costs are quite extensive & will not be worth it unless you have to replace an old system.
You actually heat a 3 car garage with electric!! Decadent bugger. You don't need to save money with Geo thermal

I've learned quite a bit since I originally posted this message. Just to clear up a few things, my garage is not heated with electric it is tied in to my home boiler, but there is an electric water heater for domestic hot water.

I have measured my overflow at 3 gal/minute and 50 degrees. I have purchased a 500 gallon underground plastic storage tank that I will fill with the overflowing well, and install an overflow on the tank that will fill my pond. I am going to install 100ft of 1" thin wall copper in a coil and connect it to a cold water chiller device that unico makes for my air handler. I will have a closed loop system that circulates through the copper coil, then to the air handler. This should take care off my cooling and I will no longer need to run my 60,000 BTU AC compressor. The heat will be the next part and a bit more tricky and expensive I imagine. If I can get someone to design me a heat pump system that uses my existing oil boiler for backup or augmentation I'll be willing to try it out. even if I just use the heat pump to preheat the return from the radiant before it goes into the boiler, I imagine that would be pretty helpful.

Fletch - you DONT want to run cold water through your floor or radiators for one main reason.  Cold water will obviously cause the surfaces it contacts to get cold.  Cold things (a glass of iced-tea) get condensate on them, as they cause the air around the object to hit its dewpoint and "rain". 

So, if you run cold water through your floor, be prepared for wet or "sweating" floors.

I would recommend a geothermal heat pump.  It can extract the heat out of the well water for heating, and use the chilled water to cool the condenser in cooling.  Check out http://www.hydroheat.com/geoworks.htm to find out more.

You won't get much out of that for cooling. Keep in mind a Btu is the amount of heat required to raise the temperature of 1 pound of water by 1 degree F. So, if you raise the temp of the water 10F, which you could with a heat pump used for cooling, this gives you 3 gpm x 60 min/hr x 10F x 8.54 lbs/gal = 15,372 Btuh. Same thing for heating if you extract 10F of heat from the water.

Several water to water heat pump mfrs have techical data on their units available on their web sites. Take a look at some of those and you'll get an idea of how much you might be able to use your available supply for heat and cooling.

How large is your pond? You might be able to put a loop in it and use it for your heat source and heat sink. The advantage to that is the well water is flowing into it 24 hrs a day and so provides quite a storage or surge supply. That way you aren't limited to the what the 3 gpm flow can handle.

Dmaceld had a good point.  a company by the name of AWEB supply makes a pond Hx for geothermal heat pumps.  as long as the pond is 14' deep or so, you may be in luck.  AWEB can help with the sizing of the heat exchanger as well. http://www.awebgeo.com/AWEB.asp?file=SlimJim.asp 

Good luck -