To figure this accurately, you must know how much you’ll save each year in energy costs with a geothermal system as well as the price difference between it and an ordinary heating system and central air conditioner. As an example: If you’ll save $700 per year with a geothermal system and the price difference is $2,000, your payback will be less than three years. If you install a geothermal system in a new home, the monthly savings in operating costs generally will offset the additional monthly cost in the mortgage, resulting in an immediate positive cash flow.