If there is an adequate body of water on your property, a water-source heat pump may be your lowest-cost option. The body of water should be at least .5 acres within a minimum depth of 8 feet to see maximum results.
A supply line pipe is run underground, from your home to the body of water, and connected to a loop exchanger: either coils of pipe, flat plate heat exchangers, or a variety of new technologies. It is not typically recommended for it to rest on the bottom of your pond or lake, but rather it should be raised 1-2 feet to ensure it stays uninhibited from plat growth or silt.
A pond or lake loop system may be designed and constructed in many ways; however the underlying principal remains the same for all. Water, in its “heaviest” state, should be 39 degrees Fahrenheit and should rest in its own isolated temperature layer at the bottom throughout the year. This is where the loop exchanger is ideally placed and is most efficient.