Radiant floor heating systems heat a room by means of a system of pipes or wires that run beneath the surface flooring to gently radiate heat upward into the room. Such systems offer a good way to heat a room addition where it is difficult to extend existing HVAC ductwork, and they are especially effective on flooring surfaces that are naturally cool to the touch, such as stone, concrete, or ceramic tile. Radiant floors can also be a good choice in large, tall rooms since the heat source emanates at floor level, where the heating is most needed. And particularly in rooms where you walk with bare feet (the prime example is a bathroom), a radiant floor makes for unparalleled comfort.
Radiant floor systems come in several styles, but one of the most popular is the electric system, in which a wire mesh or loops of individual wires run across the floor beneath the surface, creating warmth by means of the natural resistance occurring as electricity flows through the metal wires.
Anatomy of an Electric Radiant Floor Heating System
The principle of radiant floor heating has been around for centuries. In ancient Rome, for example, many public buildings had a system of tunnels beneath stone floors that circulated air warmed by wood-burning fires. In the modern electric adaptation, thin heating cables installed under surface flooring—most commonly ceramic tile—heat the floor much the way an electric blanket works. Typically they are operated by their own 15- or 20-amp electrical circuit controlled by a wall thermostat. Often such systems are used to provide supplemental heat and are installed during remodeling projects.
Most electric radiant floors involve laying strips of electrical matting across the subfloor, linked together and connected to an electrical circuit and line-voltage thermostat, and secured in place by a covering of thin-set mortar. The surface floor covering is installed over the electrical matts. In these matt systems, you can cut pieces to size to fit irregular areas, although it is generally better to use full-sized mats. Ideally, the mats cover most of the floor, but it is also possible to confine the heating to areas where you usually walk. In other systems, individual wires are looped across the bathroom floor about 3 inches apart and secured by thin-set adhesive. For ceramic or stone tile floors, the electrical mats or wires are installed over the cement board underlayment, over which the ceramic tile is then laid.
Electric radiant heating systems buried within thermal masses (such as between cement board and ceramic tile) can retain heat for a long time, even after the power is turned off.
Electric radiant floor systems offer a discreet way of heating a floor. With the right temperature setting, it is difficult to even detect that the radiant heat is operating.
These systems are ideal for use under naturally cool surfaces, such as ceramic and stone tile or on concrete slabs.
Electric systems are easy to install during remodeling projects.
Radiant systems, in general, are more cost-effective than other means of electric supplemental heating, such as space heaters.
Electrical systems are the most DIY-friendly of the radiant floor options.
These systems are difficult to install retroactively, as the floor covering must be removed. They are most practical during new construction or during major remodeling projects.
They are more effective at warming the floor surface "to the touch," rather than heating the entire room (though it is possible to use radiant floor heating as your primary heat source).
For whole-home use, electrical systems are more expensive to operate than warm-water radiant heating.
Broken wires are trapped between flooring surfaces and are difficult to locate the broken or shorted wire and even harder to repair.
Radiant floor heating is less effective under carpeting, hardwood, or vinyl since heat can be trapped between the insulating surface layer and the subfloor.
You can expect to pay at least $8 per square foot at a minimum for the materials for an electric radiant floor. For estimating purposes, $10 to $12 per square foot is a safe number to use for materials alone. On average, for professional installation plus materials, plan on spending about $16 per square foot.
While it depends on where you are located and the cost of electricity there, you can figure on operating costs of about $0.50 to $1.00 per day for an 8 x 10-foot bathroom, if the system runs 24 hours a day (regulated by thermostat). When operated 8 hours a day, costs run about $0.25 to $0.35 per day for the same 8 x 10-foot bathroom.
Alternate Forms of Radiant Floor Heating
Less common but also available is the hydronic (hot water) radiant floor system. In hydronic systems, tubes of water warmed by a central boiler or hot water heater circulate beneath the floor. Hydronic radiant floor systems are more typically used in new construction for creation of whole-house heating systems. Installation costs are considerably higher than for other central heating systems, but hydronic radiant systems are extremely efficient and offer lower operating costs over time. They are also useful for homes off the grid as they can run on a wide variety of energy sources to heat the liquid.