We thoroughly researched geothermal systems about 20 years ago, and ultimately settled on simply putting solar hot water. The payback period wasn't less than 7 years (my guideline at the time). The solar hot water paid for itself in about 2 years, and lasted 7 years, no complaints (the tank suffered from electrolysis and ultimately leaked). Given the cost of fossil fuels today, I would revisit geothermal, especially in the mid atlantic region. The only caveat would be a realistic ROI analysis.