A discarded window air conditioner has become the centerpiece of an unconventional geothermal cooling experiment after YouTuber Craftsman Chris rebuilt the machine to dump household heat into the ground instead of the outdoor air.

The project combines a salvaged 14,000-BTU LG Dual Inverter window air conditioner with roughly 2,000 feet of buried PEX tubing. After several iterations, the system is now producing supply air around 49–54°F and automatically cooling parts of the house.

Chris initially buried four 500-foot loops of half-inch PEX about 6–8 feet underground. The original system circulated groundwater through a heat exchanger in the home’s furnace plenum, but the approach was limited by the temperature of the ground-loop water.

The new design uses the same buried loops in a different way. Instead of sending the relatively cool water directly through the house’s air-handling system, the water now cools the condenser of a conventional refrigerant-based air conditioner.

Chris salvaged an LG 14,000-BTU Dual Inverter window unit from a dumpster and cleaned its heavily contaminated coils and internal components. Crucially, he kept the refrigeration circuit sealed rather than cutting the copper lines and recovering the refrigerant.

He then rotated the condenser coil by roughly 90 degrees and built a water jacket around it from scrap sheet metal. Ground-loop water enters the jacket, surrounds the condenser, absorbs heat rejected by the refrigerant, and then travels back through the buried PEX loops. That effectively turns the window unit into a rudimentary ground-source heat pump.

Getting the refrigeration system and ground loops working was only part of the challenge.

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