This paper describes the thermal performance of the third in a series of five affordable, near zero-energy house prototypes built in Lenoir City, Tennessee. This house features structural insulated panels, geothermal space heating and cooling, and a 2 kWp grid-tied photovoltaic system. The cost to conduct this research house in 2004 was around $100,000, and in 2005 it had a net daily cost for off-site energy of only $0.79 (based on the local electric rate of $0.068/kWh). This all-electric house was heated and ventilated according to ASHRAE Standard 62.2 in the winter of 2003–2004 for less than $40.