Radiant heating comes of age: it's pricey but efficient ... and very cozy.

Dig three or four feet into the ground and the earth is a constantly temperate place. Beneath that upper layer, it's a dependable 54 degrees, give or take, making geothermal systems for radiant home heating a reliable source of heat exchange.

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In a closed-loop system, a liquid (usually water or a mix of water and antifreeze) circulates from the ground into a boiler and then through piping installed under flooring to create warmth that radiates upwards to heat interior space. It's especially popular in bathrooms to warm cold tile floors under bare feet. But radiant heat can go anywhere, even under hardwood and carpet.

Once touted as the future of green home heating, whole-house radiant heat is now largely considered a luxury item or upgrade. It is most useful in climates without summer humidity and winter chill, since steamy summer days call for the dehumidifying and cooling of air conditioning, and dry winter cold requires humidifying and additional heat to make interior spaces livable. Some companies that arose during the last building boom as green energy providers have moved away from radiant heating entirely, shifting their focus to solar and wind power for all home applications.

"It's typically just a supplement," says Colin Williams, operations director at West Virginia-based Mountain View Solar & Wind, a company that once focused on radiant heating systems but jettisoned its building division when the housing market turned.

According to Williams, whose company operates in largely rural areas, a closed-loop system for radiant heat adds about $25,000 to the cost of a new build. In urban Washington, D.C., contractor Richard Mandell of Sandy Spring Builders (sandyspringbuilders.com) says the added cost is more like $50,000.

The Coziness Factor

Mandell's company builds multimillion-dollar custom homes for which a radiant system is a conceivable upgrade. The comfort of radiant heat is unquestioned; it produces a cozy warmth. "People love it," Mandell says. "Radiant heat is warm, even and just a wonderful feeling in a house."

At Mandell's vacation home in Colorado, radiant heat is all there is. Because the area is dry in summer and the temperature doesn't drop too severely in winter, the system is sufficient. "The house is cozy all winter long," he says. The system even extends under exterior walkways and pavement, so they never chill deeply enough for snow to stick.

Such radiant heating systems are inherently efficient because water at 54 degrees doesn't need to be made much hotter before it circulates under floors. Consumers interested in green building look to radiant heat as a long-term investment in lowered energy consumption.

"Everybody comes to us wanting to be green," Mandell says. Depending on their budget, the choice becomes whether to install radiant heating or simply select an upgraded home energy system and good insulation.

Radiant's Long Reach

There's nothing new about radiant heating. Any historic home will likely still have its original cast-iron radiators, some of which are quite ornate, which rely on the same principle of circulated water to heat interior spaces. Old radiators were clunky, dusty and occasionally loud, with air bubbles causing banging sounds when the heat kicked on.

In the mid-1930s, with the development of the electric fan, radiant heat was replaced with forced-air systems using ductwork which remains the standard in building today. However, updated wall-mounted or baseboard radiant systems are still available and offer efficiencies that integrated systems do not.

Installing panel radiators along outside walls or near windows puts heat "where your heat loss is," says Owen Kantor, vice president of Runtal Radiators (runtalnorthamerica.com), a Swiss-based company that has been making radiators in the U.S. for 25 years. Also, he adds, it is quicker and more efficient to raise the temperature of a single room using a panel or baseboard unit than by heating water under the floor.

Even more efficiency can be had by employing a radiant-heat towel warmer in bathrooms, according to Kantor. In some cases, it alone can warm the bathroom. With today's radiators offering international design, "in contemporary homes, they really can become a focal point," Kantor says.

And individual radiators are far easier to add to an existing house than a floor system for homeowners that intend to retrofit for radiant heat. Putting a floor system into an existing structure can mean raising floors, reframing walls and lowering ceilings, all of which is both challenging and costly.

MAGGIE WOLFF PETERSON is a writer in Virginia whose pieces have appeared in Women's Day and Newsweek.