Geothermal energy recovery from abandoned flooded mines provides a viable high-tech solution to reuse the abandoned mines for meeting humanity’s energy needs worldwide in an environmental, economic, and reliable way. This unique energy application with mine water in the U.S., however, has not been reported. This study reports on a real geothermal energy application in the U.S. for the use of water in flooded mines for house heating. First, the site exploration of a typical flooded copper mine in the Upper Peninsula of Michigan is presented to discuss three essential components of the proposed large-scale energy application, i.e., bedrock geology, mining background, and energy reserve analyses. Then, the key technical details and data monitoring of a demonstration project for the use of mine water for heating a 15,000 ft2 (1394 m2) building are introduced. For the energy reserve, energy reserve analyses were conducted considering the renewability of the thermal energy in the natural system, which was usually neglected in the literature. The analyses revealed that the annual extractable energy from the explored flooded mine with the energy replenishment is comparable to the annual energy generated by a small-scale power station, which can support over 82,000 households. The results from the demonstration project indicated that house heating with geothermal energy via the mine water is the most efficient and the second most economical heating option in very unfavorable conditions with a high electricity price and a low annual average air temperature. The intention of this study is to share the background and practical knowledge that has been learned from this ongoing project to guide future real installations in other mining areas with deep flooded mines in the U.S. and around the world.