In a radiant setup, the warmth is supplied by hot-water tubes or electric wires buried underneath the floor. As the invisible waves of thermal radiation rise from below, they warm up any objects they strike, which radiate that captured heat in turn. Though the air temperature remains relatively constant, you stay comfortable because the surrounding surfaces aren’t stealing warmth from your body.
Contrast that with what happens in a conventional forced-air heating system, the kind found in most American homes. Air blows out of the registers at a well-baked 120 degrees, rises to the top of the room where it quickly sheds heat, then drops back down as it cools. The air in the room becomes uncomfortably stratified: Your head can be bathed in warmth while your toes lie in the frozen zone. Then there’s the problem of cycling.
The result is a phenomenon called “the cold 70,” which is what you feel right after the hot air stops pumping from the registers. Those jarring ups and downs are absent with radiant floors, which may reach 85 degrees, tops, on a frigid day. The warm air still rises, but it does so evenly over the entire floor, so the coolest air stays up at the ceiling.
There are two basic ways to supply this gentle, even warmth: hot water or electricity. Electric radiant, which uses zigzagging loops of resistance wire, is generally retrofitted to a single room, such as a bathroom or kitchen. (See “The Floor Electric,” above.) Hot-water “hydronic” systems—the most popular and cost effective way to heat an entire house