Foundation heat exchangers (FHXs) used in residential ground source heat pump systems represent a potential cost savings due to their lesser first cost over other types of heat exchangers. By simulating a foundation heat exchanger system for two low-energy house constructions in seventeen United States locations, a preliminary map detailing the feasibility of FHX systems in the United States has been developed, with most of the country showing at least marginal feasibility for the technology. The FHX simulation process uses decoupled models of house and basement; the coupling between the two zones creates a difference of around 1.0°C (1.8°F) in the simulated maximum or minimum heat pump entering fluid temperature. Additionally, the operation of an FHX in the soil around a house was found to have a negligible impact on soil freezing near the house foundation. The FHX simulation needs a fully coupled house/basement model, as well as the capacity to handle snow cover, to be even more robust.