When it comes to cheap, renewable energy, nothing seems more reliable than sucking heat from Mother Earth. Geothermal heating and cooling has been around for 20 years or more, but it remains unknown to most people—we didn’t know about it until a friend installed it, and neighbors hadn’t heard of it until a huge drilling rig began the noisy, two-day process of boring holes in our small back yard. Four holes are bored into the earth – a very noisy process that takes special equipment and space to dig. Closed loops of plastic tubing now fill the four, 200-foot-deep holes.

A mix of water and refrigerant (eco-friendly, of course) will soon pump through the tubes, returning to the house at the steady temperature of 55 degrees Fahrenheit, which is the ground temperature in most parts of the country. That’s chilly enough to cool a house in the summer, while compression will raise the fluid’s temperature to heat a house on cold days. The conditioned air will circulate through conventional, forced-air ducts. Geothermal should cut heating and cooling bills in half or so. Another advantage is more subtle, but still attractive: The geothermal air moves steadily and quietly. Additionally, the outside elements of a conventional AC go away; there will be no compressor sitting along side the house.

The biggest disadvantage of geothermal heating and cooling is cost - about $10,000 to $20,000 more than a conventional system (most of that difference lies underground in those four holes). Even with today’s inflated energy prices, it will take several years for payback. And the cost might be prohibitive for someone with a system that’s working well, and has a good contractor with high efficiency equipment to professionally install.