Forced-air heating works by sending furnace-heated air through ductwork and into the living spaces. The catch? Hot air doesn't always go where you want it to go. In fact, as you remember from school, warm air rises. This means that soon after entering a room, warm air floats up to the ceiling, leaving the temperature as chilly as ever down below. What does the homeowner do in response? She turns up the heat, of course—and in doing so, drives up the energy bill. Fortunately, not every heating system relies on the movement of air. Radiant floor heating, for instance, operates via thermal radiation, which concentrates warmth not way up by the ceiling where you can't feel it, but instead right where you need comfort the most.