With a hydronic floor heating system, hot water circulates through lengths of tubing that loop back and forth on the subfloor. The tubing is usually encased in a slab of concrete or lighter-weight gypsum cement. In some cases, the tubing can be fastened to the underside of subflooring instead.

A clear advantage of hydronic systems over other forms of heating is that you can use a variety of energy sources to heat the water: a gas water heater, electric boiler, wood boiler, heat pump, solar collector, or even geothermal energy. If in a few years your heating source, such as oil for a boiler, becomes too expensive, you can change over to solar or some other source. Another advantage is that the water retains residual heat longer than electric wires.

The heated water warms floors to about 85 degrees Fahrenheit or cooler (it generally feels similar to a tile floor warmed by direct sunlight). A zone control adjusts floors of various rooms to the desired temperatures.

Hydronic heating's reputation was tarnished in the 1940s and 1950s when temperature control was marginal and metal piping corroded, leaving leaky pipes that were difficult, if not impossible, to repair. But manufacturers of today's water-circulating systems have learned from those mistakes and taken advantage of modern technology and materials to produce high-quality, low-maintenance systems. These utilize sophisticated control manifolds and polybutylene or synthetic rubber tubing that has proven its durability under extreme testing.