Even though the air temperature is cool, you can feel warm because the sun's radiant energy warms your body directly. Radiant floor heating systems today use hot water to warm your home. It utilizes tubing under the floor to carry and disperse the heat. In modern floor systems piping is normally buried in a concrete slab. Hot water is then run through the piping thereby warming the floor.
Heat then radiates from the floor warming the room and occupants.
Because the heat originates at the feet, the direct contact warms the lower extremities, giving the occupant overall comfort. Because radiant heat warms the body as well as the air, people can feel comfortable at air temperatures several degrees cooler than with other heating systems. Additional benefits include a reduction in air movement and floor to ceiling temperatures. This means that heat doesn't rise to the ceiling, above the comfort zone. And less air movement means fewer drafts and dust around the house.