Mar 5 - McClatchy-Tribune Business News Formerly Knight Ridder/Tribune Business News - Thomas C. Palmer Jr. The Boston Globe

Geothermal heating and cooling isn't just for big commercial buildings and multifamily housing complexes, specialists say.

"One question I get asked all the time," said Mike Zimmerman, who has been designing geothermal systems for almost 10 years, "is, 'If it's that efficient, why isn't everyone doing it?' "

Zimmerman admits he doesn't know for sure why geothermal, even with the current widespread popularity of green technologies, hasn't caught on with owners of single-family houses. But part of the reason is that oil and gas prices needed to reach a certain threshold before homeowners rejected the old way of doing things, he said.

Also, "there's a lot of ignorance about what is the right way to do it," Zimmerman said.

The principal is the same for residences as in larger projects -- using the constant, 50-to-55-degree temperature of the earth to cool or heat the home -- but the details of these complex heat-exchange systems vary.

"There's a lot of projects that don't work," he said. Early systems using ground water employed copper pipes, which corroded and failed. Also, drilling the wells is the most costly part of installing a geothermal system, and some installers or owners didn't put enough wells in to do the job.

"Not understanding the way thermodynamics work and overestimating the capacity of a well is a problem," Zimmerman said.

But technology and expertise have improved, and more homeowners are putting the earth's constant, dependable underground temperature to work for them.

Zimmerman said the additional cost of installing a geothermal system in a large new house of about 4,000 square feet would be $15,000 to $20,000. That would include a single well 1,000 feet deep or less, depending on geological conditions. And the house would not require a conventional furnace, an additional saving.

To retrofit an existing suburban house, Zimmerman and another geothermal specialist said, would cost a little more, an estimated $20,000 to $25,000.

The payback for converting an old house to geothermal, in energy costs saved, is 5 to 10 years.