http://www.youtube.com/watch?v=q9DP6v0IW1k&feature=player_embeddedSince they guarantee the heat exchanger pipes for 50 years, this is really a lifetime investment.It's ALWAYS around 55 degrees F under your house, winter at 10 below or summer at 90 above. This is an IDEAL solution for renewable energy because it mainly functions by AVOIDING energy use, not simply ramping up a system to whatever square feet you want in a house.
OF course if the house is already there and is huge, the system will cost plenty. However, if the government provides low interest financing for new houses of a reasonable amount of square feet (about 1,000 for a two person household) as well as financing for refurbishing old SMALL houses with a "pay as you SAVE on fossil fuels" long term payment, everybody could embrace this technology and kill heating oil once and for all.
Of course furnace manufacturers and fossil fuelers won't be too happy about it.