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One word describes radiant floor heating: friendly. When you step out of the shower or climb out of bed, it offers your bare feet a toasty welcome. It warms you silently, invisibly, economically and, unlike forced-air heating, doesn't stir up dust or allergens.

Radiant-floor heating systems utilize either hot-water or electricity to warm the floor. This heat radiates upward to provide general, even warmth. With radiant heating you can be less concerned about warm air escaping when you open a door-- though you still feel a draft, radiant heat recovers quickly because it warms your body and other objects rather than just the room's air. This fact also allows you to keep the thermostat turned two to three degrees lower than normal without losing comfort, a principle akin to standing in the warm sun on a cool spring day.

Radiant heating cuts down on heat loss through infiltration; forced-air heating pressurizes a house, pushing warm air out through cracks and openings. A home heated solely by radiant heat isn't under pressure so room air stays inside.

Radiant floor heating is more expensive to install than forced-air and related systems, but well-designed radiant systems can pay back these costs in energy savings in a few years. You'll notice the pay back in comfort immediately.

Of course, radiant heating is just that-- heating. These systems do not cool or clean the air. If you live in a climate that calls for cooling, you'll need additional equipment to handle the job--perhaps zone air conditioners or, better still, a heat pump that both provides cooling and heats the water of a hydronic radiant system.

Hydronic systems are typically the best choice for new construction; electric-resistance heating lends itself to new room additions or small projects calling for minimal installation costs. On the following pages, you'll find a closer look at these two main types of radiant heating systems.

Hot-water-circulating (hydronic) systems
With a hydronic system, hot water circulates through long lengths of tubing that loop back and forth beneath the floor's surface. The tubing is either encased in a slab of concrete or lighter-weight gypsum-cement or they're stapled to the underside of subflooring.

A clear advantage of hydronic systems over other forms of heating is that you can use a variety of energy sources to heat the water: gas water heater, electric boiler, wood boiler, heat pump, solar collector or even geothermal energy. If in a few years your heating source-such as an oil boiler-- becomes too expensive, you can change over to solar or some other source.

The heated water warms floors to about 85 degrees F or less (it generally feels similar to a tile floor warmed by direct sunlight). A zone control adjusts floors of various rooms to the desired temperatures.

Hydronic radiant's reputation was tarnished in the 1940s and 50s when temperature control was marginal and metal piping corroded, leaving leaky pipes that were difficult--if not impossible--to repair. But manufacturers of today's water-circulating systems have learned from those mistakes and taken advantage of modern technology and materials.

They utilize sophisticated control manifolds and polybutylene or synthetic rubber tubing that has proven its durability under extreme testing.

Electrical-resistance systems
Two categories of electrical radiant-floor systems are manufactured: 1) cable and 2) flexible foil sheeting or rigid panel systems. With cable systems, a special electric heating cable winds back and forth, embedded in a concrete or gypsum-cement slab. Flexible foils are stapled between floor joists or laid between joists on top of fiberglass insulation; rigid panels are hung on straps between joists or buried in concrete slabs. When electrical current runs through the cable, foils or panels, it generates heat.

With a do-it-yourself cable system, you attach low-wattage heating cables to the subfloor then cover them with a pourable gypsum cement underlayment. The resulting floor underlayment is flat, solid and has plenty of thermal mass for retaining and slowly releasing heat. This special gypsum/cement mixture can provide a thinner slab than normal concrete without danger of cracking.

In many parts of the country, electricity is expensive compared to other energy sources. Where electricity costs are high, electric-resistance heating isn't practical. Unlike a hydronic system, once you install electrical cable or foil systems, you cannot easily change to another energy source if electricity prices skyrocket.

Be sure to look for UL approval when purchasing an electric system.