Radiant Floor Heating

Radiant floor heating has its origin in ancient Rome, where fires were built beneath the floors of villas. Early Korean buildings were similarly heated by channeling flue gases beneath floors before venting those gases up through chimneys. Frank Lloyd Wright piped hot water, rather than air, through the floors of many of his buildings in the 1930s—a practice that has become common in custom homes today.

How radiant floor heating works

Radiant floor heating turns a floor into a large-area, low-temperature radiator. In most modern radiant floor heating systems, warm water circulates through plastic tubing either embedded in a floor slab or attached to the underside of subflooring. With slab systems, one can use either a standard concrete slab-on-grade, or a thinner, lightweight gypsum-concrete slab poured on a subfloor or over an existing finished floor. In either case, the thermal mass of the slab holds heat and radiates it slowly to the living space above.

In addition to hot water as the heat source, radiant floor heating can also use electricity or hot air. Due to the high cost of electricity in most areas, radiant electric floor heating usually makes the most sense when off-peak electricity is available for charging a slab at night and during other off-peak hours. Production of electromagnetic fields (EMFs) is also a potential concern with radiant electric heating. Radiant air floors are occasionally used in commercial buildings but are generally impractical and too expensive for residential applications.

Hydronic radiant floor heating

For hydronic radiant floor systems, copper piping has been used in the past, but most systems today use either rubber or cross-linked polyethylene (PEX) tubing—the latter being by far the most common. Design of radiant floor heating systems is quite complex and should be done by someone with adequate training or experience. Various design manuals, manufacturer-specific installation guides, and software tools are available for use in designing and sizing radiant floor heating systems.

The length of tubing required per square foot of floor depends on such variables as tubing diameter, type of radiant floor system (thick slab, thin slab, no slab), climate, heat load of the building, and type of boiler and controls used. Manufacturers have done a great job in recent years in packaging the various components to simplify the design of radiant floor systems.

A key requirement for most radiant floor heating systems is adequate insulation beneath the heated slab or beneath the tubing (when tubing is attached to the underside of a subfloor). Most manufacturers recommend a minimum of 1" (25 mm) of extruded polystyrene (XPS) for concrete slab-on-grade radiant heating systems, but significantly higher levels are justified in cold climates.

Zoning of radiant floor heating

Zoning of radiant floors is usually done with advanced manifold modules that allow the water temperature to be varied in different zones. This provides flexibility for maintaining different temperatures in different rooms and for allowing differential heat delivery to spaces with and without solar gain.

Finally, sophisticated controls are often installed to ensure optimal comfort and to maximize energy performance. Some radiant floor systems rely on separate temperature sensors outdoors, within the floor slab, and in the living space—with microprocessor control to regulate just when and where hot water should be delivered. Because of the long lag-time with concrete-slab radiant floor heating systems, standard set-back thermostats usually are not effective, though set-back thermostats that have a built-in anticipation feature may work well for this application.

Radiant Floor Heating copyright 2011 Digtheheat.com