Robert Hoffmann and his brother Tom have made a business of helping homeowners realize the energy potential in their own yards. More accurately, under their yards.

Not drilling for oil, or even installing a wind turbine. Instead, the Hoffmann brothers specialize in geothermal energy — literally tapping the relative constant temperature of the earth to heat and air-condition homes and offices.

The brothers have owned Hoffmann Brothers Heating and Air Conditioning since 1988, when they bought out a small HVAC contractor, Linton Heating & Cooling.

The company has grown from four employees to more than 45 and in recent years has developed a specialty in geothermal energy systems.

The Hoffmanns already had some experience installing geothermal systems, and saw a market ready to accelerate in 2008 when the government began offering tax credits for 30 percent of the cost of systems.

Today, the company installs up to five systems a week, including large ones that cost hundreds of thousands of dollars.

For Hoffmann, the brilliance of geothermal energy is its efficiency. The upfront cost of systems can be a drawback, but in many cases they pay for themselves within a few years, he said.

"People brag about their 95 percent efficient furnace, but you can't beat a geothermal system," he says. "It doesn't even compare; it's on a different scale."

How does a geothermal energy system work?

The ground is like a huge battery — in the wintertime you're just sucking it dry of the energy and in the summertime you're doing the opposite. You're taking the heat from the house and you're putting it back into the ground. So it's kind of a neat concept. You're just using the ground as a huge storage device. Also in the summer, instead of putting it into the ground, we put it into their hot water, so we can heat their water with the waste heat off the geothermal system.

What does a typical residential geothermal system cost?

They are typically around $7,000 per ton for replacement geothermal heating and cooling. So if a typical house is 3 tons, its $21,000. The cost would be for drilling equipment, backup heating, the water heater, the whole nine yards.

And how much does a geothermal system save on utility bills?

I'll give you a typical scenario. Somebody is trying to decide: "Do I put in geothermal, or do I put in a high-efficiency heating and cooling system.?" They have a 4-ton unit.

A 4-ton geothermal system is going to cost you $27,000. A regular system may cost you $11,000. But on the geothermal, you're going to get about a $9,000 (federal ) tax credit; you're going to get some money from Ameren (Missouri); they have a program. And there currently is a program, that's about to end, from the state of Missouri where you can get up to an additional $10,000 on top of all that. But that program is almost out of money. It's called Energize Missouri.

So you're down to really comparing $11,000 versus $18,000, and you're trying to justify the difference there — $7,000. The savings is about $1,800 a year in that particular example, so just in a few years you've got your money back.

Why aren't more people doing this?

It's the upfront cost. We used to be able to approve 80 percent to 90 percent of all the applicants that came in for financing, and now we're able to approve 40 percent. The banks have gotten much tougher.

But if you're going to make a 25 percent return on the geothermal system, you can afford a 9 percent loan. Its cheaper in the long run because you're going to save more than what your interest is going to be.

St. Louis has so many older homes. Is it tougher to install these systems on older homes than with new construction?

We do mostly old homes and it is a little bit harder, not that much. The big thing people don't realize is the insulating value in the home is key. If somebody's house does not have an insulated basement, that is a tremendous heat loss. In the wintertime there is a tremendous amount of loss.

What that does is, that (loss) will increase the size of the unit by a ton, so you'll go from a 3-ton to a 4-ton unit, and that'll add $7,000 to your cost. Wouldn't you rather just put that $7,000 into insulating those basement walls instead of buying a bigger geothermal system?