DIY Ground Heat Pumps

Calculate the heat pump capacity needed for your project. If it is a new residence, you may have to hire a professional to perform a heat survey. For an existing home, find the heat output of the existing furnace in kilowatts or British thermal units (BTU) per hour. Multiply the kilowatts by 3,412 to get BTU. Divide BTU by 12,000 to get tons of heat pump capacity.

Rent a backhoe or hire a contractor to dig the ditch 6 feet deep and at least 1 foot wide. Check with the heat pump manufacturer to get the length of piping needed for the heat pump, usually about 400 feet for each ton of heat pump capacity. Dig the ditch in parallel loops at least 5 feet apart so that the ditch starts and finishes at the house.

Place the polyethylene pipe in the ditch. Heat weld the joints to get the length required. Drill holes into the basement, and feed the ends of the pipe through the holes to start and finish the run of pipe at the location where the heat pump will be installed. Pressure test the completed run with three times the system operating pressure, following the heat pump manufacturer's documentation. Backfill the ditch, taking care to remove sharp rocks that might damage the pipe.

Install the heat pump. Connect the cable to the breaker panel and wire the heat pump per the manufacturer's instructions. Fill the piping with water/antifreeze mixture as specified by the heat pump manufacturer, and connect the piping to the heat pump. Follow the heat pump manufacturer's instructions for flushing the pipe run by running the outside loop pump for at least 15 minutes and purging any air that is present.

Install and connect the forced air ducting. Size the main air duct according to the size of the output air manifold of the heat pump. Run several branch ducts to each major room, and one branch duct to each bathroom. Install a cold air return for each major room. Start the heat pump and run startup tests per the manufacturer's recommendations.