St. Louis' temperate climate makes the region an ideal ground zero — so to speak — for geothermal heating and cooling systems that drastically slash home energy costs, experts say.

Among the growing number of users here is Gary Pedersen, a retired Bayer Corp. policy analyst. He says the utility costs at his two-year-old Kirkwood home are half those at his nearly identical former home in Eureka, which had a conventional forced-air system.

Pedersen, 69, said his geothermal system "was a little bit more expensive, but over the long run it will more than pay for itself."

Architects, builders and engineers familiar with geothermal systems said this part of the Midwest has limitless potential for low-cost heating and cooling.

Geothermal energy currently provides a sliver of the nation's residential needs. But if enough homes use free energy stored in the earth, utilities will no longer need to continue building costly and polluting power plants, geothermal advocates say.

Among them is Yunsheng "Shawn" Xu, an associate professor of engineering at the University of Missouri who is designing a geothermal system to drop his home's energy costs to zero. He will install the system in his family's house, which he plans to start building next month west of Columbia. Xu (pronounced "shoe") met this week with the project's architect, Tom Tyler, founder of Answers Inc., and one of the home's builders, Matt Belcher, president of Belcher Homes, both of St. Louis.

Orienting Xu's 2,600-square-foot home on the 15-acre semirural site to make the best use of the sun's effects and figuring out where to place rooms consumed part of the meeting. Xu, 47, is in charge of the home's geothermal system.

It will be infinitesimally smaller than the ones he helped design for the Olympic Village and the 91,000-seat "Bird's Next" stadium built for the Beijing Games last year. Huge or small, geothermal systems are simple. They work like this:

— A fluid — mostly water — circulates through coils of plastic pipe placed horizontally a few feet below the ground surface or in holes bored 150 to 200 feet deep.

— In winter, the fluid warmed underground is pumped from the earth and after heated further by a compressor is distributed through a building's conventional duct work.

— In summer, the process is reversed. The geothermal coils return the building's interior heat to the ground, much the way a refrigerator sheds heat through its coils. The rule of thumb is that a geothermal system is at least 70 percent more efficient than a natural gas furnace.

Experts say the St. Louis region is especially geothermal friendly because its infrequent triple-digit temperature swings over a given year mean the ground temperature just a few feet below the surface is a constant 60 degrees or so. As a result, heating and cooling demands on a geothermal system are low.

Xu will bury geothermal coils beneath his home's gravel driveway and boost efficiency with a solar panel that will provide the electricity needed to power the system's small pump. Lots of wall and roof insulation, plus moveable exterior window blinds also will help cut reliance on utility-supplied electricity to zero, he said.

"It'll be nice," Xu added.

He said the geothermal system's cost — roughly double that a conventional heating and cooling system — helps push his three-bedroom home's construction budget to about $400,000. At about $154 per square feet, the cost remains solidly in the range of custom-built homes in the St. Louis area. He plans to recoup 30 percent of the geothermal system's cost through the federal tax credit that applies to geothermal systems as well as solar panels, solar water heaters, small wind energy systems and fuel cells.

Tyler and Belcher predict the number of geothermal homes in the St. Louis area will grow. St. Louis has "a certain sense of practicality that allows it to adapt some of these technologies," Tyler said. In the St. Louis area, using the earth to heat and cool homes is more efficient than trying to do the job with solar or wind energy, he added.

Belcher said a few local lenders are beginning to realize that geothermal systems enhance a home's value. St. Louis electricity costs are relatively low but will inevitably rise, making super-energy-efficient homes even more desirable, he added.

"Every time Ameren talks about bumping its rates, it seems like my phone rings a little more often," Belcher said.

How many geothermal systems are in homes nationwide is difficult to determine, but according to the National Association of Home Builders, the number has grown in the past two years, said Calli Schmidt, an association spokeswoman.

The government's Energy Information Administration reported in July that of the nearly 100 quadrillion BTUs consumed in the United States last year, 7 percent came from renewable energy sources. Of that amount, 5 percent came from geothermal energy. Though still small, geothermal energy use doubled between 1995 and 2007, the Census Bureau has reported.

Pedersen said he and his wife, Sharon, appreciate their system's lack of a noisy outside air-conditioning compressor and the whisper of quiet fans that gently move air to and from the geothermal coils. Summer cooling costs are low, and "in the winter, we pretty much get everything out of the earth," he said.