Underground Thermal Energy Storage (UTES) has emerged in both specific applications and within energy policy literature as a promising technology for meeting thermal loads with locally collected and stored solar energy, as well as several other potential applications, such as time-shifting of grid-based wind and solar power to better align variable generation with loads. In Europe, UTES systems have experienced increased deployment in connection with district heating systems. But despite this academic attention and several demonstration projects, the commercial market viability of UTES systems has yet to be established in North America, and the finance world uses different conceptions of viability than engineering or academic studies. This study explores, through the conventions of finance and risk mitigation, what capital costs North American UTES systems would need to exhibit to achieve market viability; which is to say, the investment cost at which a UTES system represents an attractive investment when compared with natural gas-based systems for the provision of residential space heating. (C) 2018 Elsevier Ltd. All rights reserved.