Central radiant floor heating (Hypocaust) was first used in the Roman times where hot air was circulated in spaces below floors and behind walls in public bath houses and large villas. Soon it was realized that hot air as a heat transfer medium is far from ideal. Water on the other hand has the highest heat capacity per volume in any liquid and commonly used materials. Once this discovery was made, it wasn’t long before pipes carrying hot water were embedded in floors and walls , circulated by natural convection.
Convection driven heating systems were dominant until electricity was discovered and with it electrical motors and modern circulator pumps and controls. Convection driven Hydronics require relatively large diameter piping and heat emitters with low resistance to flow. Cast iron radiators and boilers, large diameter steel piping are perfect for that kind of heating. Fine tuning temperatures, higher efficiencies and less obtrusive appearance of such a system is problematic at best.
With the advent of modulating condensing boilers, heat pumps and microprocessor driven electronics, reaching ultra high efficiencies and fine controls of hydronic radiant heating is now a reality. Floor heating is the most efficient way to heat any structure thanks to the large heated surface area and the fact that they utilize relatively low temperature water to achieve design temperatures. Condensing modulating boilers approach their peak efficiency when their output temperature is below 100°F. Baseboard heaters operate at 160°F and up, cast iron radiators the same, hydronic air handlers 140°F and up, steel fin radiators 140°F and up. No other heat emitter can get away with such low water temperatures. Heated floors’ low temperature requirements mean that they work perfectly in tandem with air to water or ground source (water to water) heat pumps.
When the floor is heated it emits infrared radiation the same way the sun is heating the Earth. This infrared radiation is in turn absorbed by objects in its path including you, then it gets partially re-emitted. The heat propagates from the ground up. As opposed to forced air heating where your head cooks and your feet freezes, the heat is where you are, on the ground not up in the ceiling. This uniform heat is achieved with no noise, no air blowing, no dust being stirred up. When you are in a room with heated floors and close your eyes, you will have trouble figuring if it is winter or summer, fall or spring outside. You just feel comfortable and forget about the season.