Nowadays, with the accelerating global energy utilization and the over-reliance on fossil resources, satisfying the whole energy demand without negative environmental impacts is challenging. Buildings consume about 36% of total global energy resulting in significant greenhouse gas emissions. An immediate shift from fossil-based systems for space heating and cooling is required to avoid the impending catastrophic consequences of climate change. Employing foundation heat exchangers (FHXs) is a non-conventional technique that uses the building foundation and underground soil heat capacity to provide space heating and cooling efficiently. When coupled with ground source heat pumps (GSHPs), FHXs can significantly address the issues associated with GSHPs, namely high initial capital costs and the absence of drilling space in densely populated areas. Compared to conventional systems, horizontal FHXs coupled with GSHPs have not been widely studied, especially in regions with cold climates. The current research investigates the thermal performance of a horizontal FHX embedded under a single-family residential building and coupled with a GSHP. A detailed transient computational fluid dynamics model is developed in ANSYS Fluent and thoroughly validated against several experimental studies. The model uses actual building energy loads together with the basement indoor temperature profile to evaluate the heat transfer rates, coefficient of performance of the GSHP, and temperature distribution of the soil. Moreover, the influence of various design parameters on performance is presented. Results show that the overall performance of the system improves by increasing either the fluid velocity or the diameter of the pipes and increasing the FHX depth.