This geothermal water heater design consists of two water tanks connected together with a water-to-water heat pump to extract heat from (or cool) the water in one tank to heat the water in the other. The hot water tank is intended to supply heated water for common domestic uses while the cold water tank is simply installed in-line to supply the home with cold(er) water. While the installation does not require any additional pipes in the ground, it is essentially a geothermal water heater because the available heat from the cold water supply comes from the ground in which the supply lines are buried.

This invention takes advantage of the fact that, within the typical ranges of temperature (60ºF) and volume that water is used (280 gal/day), the available energy in the cold water entering a building through the city water supply approximates the energy required to heat the hot water. The heat can be extracted from the incoming cold water to heat the hot water using less than one-fourth the electrical energy required to heat the water directly. This appears to contradict normal thinking by displacing natural gas consumption with electricity since it requires about three units of gas energy to deliver one unit of electrical energy; but a coefficient of performance exceeding 3.0 creates a net energy savings of this water heater compared to natural gas fired water heaters. Our invention will results in a factor of four to six improvement in energy efficiency for existing electric water heaters, but is even more energy efficient than gas fired water heaters.