Matthew Linden, co-founder of ConsciousBuild in San Luis Obispo, Calif., likes to lay concrete floors in his green homes, but it's not always an easy sell. "The only way to make it salable and palatable for the discriminating buyer is if it's warm," says Linden. "You've got to make sure they've got toasty toes."

To achieve that feeling, Linden uses hydronic radiant heat flooring. By pumping warm water through tubing that's embedded in the concrete slab, these systems radiate heat upward from ground level.

"There's nothing like waking up on a cold morning, getting out of bed, and putting your bare feet down on a warm floor," says Ron Antinori, a retired software executive who installed radiant heat floors in his Atlanta home in 2004 and has since created operating software to help them run optimally. "It's the most comfortable heat you can get."

Plus, the systems can be 10 percent to 30 percent more efficient than forced-air systems, according to the Radiant Panel Association (RPA).

And while radiant heat flooring still commands a tiny percentage of the market--estimates are as low as a fraction of a percent in the U.S.--the category has seen tremendous growth since 2000. Hydronic systems have grown by 225 percent, according to the RPA, while electric systems have increased 13-fold in the same time period.

Luxurious Options
The two main types of radiant heat flooring are hydronic systems, such as those mentioned above, and electric, which use either wired matting or coiled cables, to generate heat beneath floors.