So far, the systems are found largely in big, custom-built homes.

But developers are increasingly considering incorporating the technologies in multifamily housing developments or offering them as upgrades for single-family homes. Solar tax credits as a result of this year's federal energy bill also may provide stimulus.

Of course, Americans have heard all this before, in the last energy crisis during President Jimmy Carter's administration in the late 1970s.

But indications are that the trend has more staying power this time, partly because of technological improvements and partly because fossil fuels are depleting and more costly to find and extract.

"A lot of what we see are general concepts that have been out there for some time, but improved and tweaked," said Cory Lowe, a spokesman for the Rocky Mountain Institute, a nonprofit that promotes energy efficiency. "There's been quite a few innovations in solar panels, and solar hot water heaters are relatively cheap today."

Developers warming to idea

Wheat Ridge-based Major Geothermal is one company noticing a pick-up in business. It has done numerous geothermal projects in Colorado in the past five years, typically in custom homes or buildings ranging from 4,000 to 10,000 square feet.

"It used to be a lot of tree huggers, green people," said company President Jack Major Jr. But now, Major said, he's getting inquiries from a range of developers.

One is Paauw. Another developer is considering a ground-source heating system for lofts in the lower downtown Denver area. A third is looking at putting in a system at an affordable duplex and four-plex housing development in Greeley. A fourth is considering the technology for a hockey rink in Aurora.

"We're actually drilling today," Major said Friday. "We're switching our office (in Wheat Ridge) into a ground source."

Retrofitting, though, typically is harder to do than new construction, he said.

"You're better off insulating or putting in 90 percent (energy efficient) furnaces, go that route," Major said.

Even the geothermal energy industry has felt some negative impact from rising energy costs, Major indicated. Pipe made from petroleum byproducts is difficult to find, and prices are soaring, he said.

Still, Major is frustrated that geothermal technology in home construction isn't happening as fast along the Front Range as in Canada, Minnesota, Wisconsin or even on the Colorado's Western Slope.

"Developers of tract homes aren't the least bit interested," Major said, even though a system may add only $20 a month or so to a 30-year mortgage. "We can get the homeowner interested, but not the developer. . . . Builders fight change, but they've got to wake up, because energy costs aren't going to come down."

Kim Calomino, vice president of technical and regulatory affairs for the Home Builders Association of Metro Denver, agrees it's something more builders are - and should be - considering.

In fact, Calomino is working with Rocky Mountain Geothermal on possibly using a ground source for the association's new headquarters. Building designs are still being explored.

"It (geothermal energy) has great efficiencies," Calomino said. "You always face higher upfront costs, but the payback is relatively short compared with photovoltaics (solar power)."

But she said it would be misleading to encourage homeowners to rush out and "drop a drill" for a geothermal system or buy solar energy equipment without first taking the basic steps to tighten up their house and make it more energy efficient.

"Don't forget the basics," she said.

Cost-benefit analysis

That in part is the philosophy of Louisville-based McStain Neighborhoods, considered one of Colorado's pioneers in building "green" houses, or resource-efficient homes.

McStain's current approach focuses on building sturdy, well-insulated, airtight homes with energy-efficient windows and appliances. Insulation, for example, is blown cellulose - made from old newspapers and other recycled materials.

McStain is dabbling with solar power, such as photovoltaics, but with a more deliberate approach.

The company integrated solar in an experimental house called the Discovery House in Loveland and offers both a solar domestic hot water system and a photovoltaic solar electricity system as options, said Jeff Medanich, McStain's construction administrator and special projects manager.

But Medanich said the company learned from the Discovery House that such systems can require large water storage tanks and large battery storage capacity.

Just this week, Medanich said he got a call from a California company that is making wind power available for residences. He is studying the idea but notes that challenges include appearance, battery storage and possible resistance from homeowners associations.

Medanich said McStain isn't doing anything with geothermal at this point, "but we're certainly aware of it. It's pretty common in Minnesota. I think people (here) haven't realized the economics of it yet."

All propositions have to be weighed, Medanich said, in terms of cost vs. value.

The average family only stays in a house for seven to eight years. So if the payback on a system is 10 years, "the next guy gets the benefit," Medanich said.

McStain has decided it is worth incorporating tankless, or on-demand, water heating as standard features at its Carriage Homes development at Stapleton and at Crescent Ridge at Lowry, the latter to break ground in November.

"Instead of having a hot water tank in the basement with a flame constantly burning . . . you're only heating the water as needed," Medanich said. An open tap, he said, turns on a gas module the size of a suitcase and heats the water at a high rate.

The module hangs on the wall in a basement, thus saving floor space. Such on-demand water heating systems are common in much of Europe and Asia, although often at the point of use, such as a module on the wall of a shower, and connected directly to the tap.

Medanich said McStain will need to continue to look at all alternative strategies to stay competitive because many developers now are positioning themselves as "green" builders.

"And we believe it's the right thing to do," Medanich said. "For us it's a long-term strategy. We've known this reality (for some time) - fossil fuels are exhaustible - so we're paying attention to renewable energy sources because it's just prudent thinking."

Next up: Smaller homes

Julee Herdt believes it's more than prudent thinking but the way to go in the future.

Herdt's "The Farmhouse" in north Boulder incorporates both solar and geothermal technologies.

The project garnered a lot of attention when it was being built in 2001 because of its use of both solar and geothermal technologies to heat and cool the house, and power the domestic hot water system.

In several years of living there (the house is now for sale), Herdt said her highest monthly energy bill was $195 and a more typical bill was $30 a month from the spring through the fall. That's for a house nearly 5,000 square feet in size.

"It's really a clean, quiet way to heat a home," Herdt said last week during a break at a solar competition in Washington with her CU students. "It's all contained right there in the house and right there in the yard," cutting one's dependence on the local utility. "It would solve so many (environmental) issues."

Herdt's next goal is to integrate energy-efficient technologies into a smaller modular home in Boulder. She thinks such technologies eventually will be feasible for small homes, especially if people realize the importance of making trade-offs in order to help reduce the country's dependence on fossil fuels.

"Americans need to learn to have a little less space and enjoy that space more," she said.