Hydronic Radiant Floor Heating Systems
In-the-floor hydronic heating circulates heated water through coils of tubing that warm the floor to about 85 degrees F.
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Manifold zone control, installed in the wall, regulates the temperatures of floors of various rooms.
Tubing is embedded in the flooring. A boiler may be heated by any number of different fuel sources. A pump circulates water through the system.
Source:http://www.hometips.com/hyhw/comfort/44hydronic.html