Radiant floor heating is creating a buzz in home remodeling, yet it has been used for centuries. The Romans channeled hot air under the floors of their villas. The Koreans channeled hot flue gases under their floors before venting them up the chimney. In the 1930s, architect Frank Lloyd Wright piped hot water through the floors of many of his buildings.
Most people who own radiant floor heating feel that the most important advantages are comfort and quiet operation. Radiant floor systems allow even heating throughout the whole floor, not just in localized spots. The room heats from the bottom up. Radiant floor heating also eliminates the draft and dust problems associated with forced-air heating systems.
There are three types of radiant floor heat: air, electric and hot water. All three types can be further subdivided by the method of installation: wet or dry.
Because air cannot hold large amounts of heat, radiant air floors are not cost-effective in residential applications.
Electric radiant floors are usually only cost-effective if your utility company offers time-of-use rates. These allow you to “charge” the concrete floor with heat during off-peak hours, usually between 9 p.m. and 6 a.m. If the floor’s thermal mass is large enough, the heat stored in it will keep the house comfortable for eight to 10 hours without any further electrical input. This saves a considerable amount of money compared to heating at peak electric rates during the day.
Hydronic (hot water) systems are the most popular and cost-effective for cooler climates. They have been in extensive use in Europe for decades. Hydronic radiant floor systems pump heated water from a boiler through tubing laid in a pattern underneath the floor. The temperature in each room is controlled by regulating the flow of hot water through each tubing loop. This is done by a system of zoning valves or pumps and thermostats.
Wet installations are the oldest form of modern radiant floor systems. In a “wet” installation, the tubing is embedded in one of the following: the concrete foundation slab, a lightweight concrete slab on top of a subfloor or a previously poured slab. If the new floor is not on solid earth, additional floor support may be necessary because of the added weight. Consult a professional engineer to determine the floor’s weight-bearing capacity.
Due to recent innovations in floor technology, “dry” floors have been gaining in popularity. Much of this is because a dry floor is faster and less expensive to build. There are several ways to construct a dry radiant floor. Some “dry” installations involve suspending the tubing underneath the subfloor between the joists. This method usually requires drilling through the floor joists in order to install the tubing. Reflective insulation must also be installed under the tubes to direct the heat upward. Tubing may also be installed from above the floor, between two layers of subfloor. In these instances, the tubes are often in aluminum diffusers that spread the water’s heat across the floor in order to heat the floor more evenly. The tubing and heat diffusers are secured between furring strips (sleepers), which carry the weight of the new subfloor and finished floor surface.
At least one company has improved on this idea by making a plywood subfloor material manufactured with tubing grooves and built-in aluminum heat-diffuser plates. Such products use half as much tubing since the heat-transfer characteristics of the floor are greatly improved over more traditional dry or wet floors.
Source: US Department of Energy
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Home Remodeling Cape Cod, the Islands & the South Coast magazine
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