Electric Radiant Floor Heating: Everything You Need to Know

If you're just catching on to the benefits of radiant floor heating, you may be discouraged by the upfront costs involved with installing hydronic (hot water) systems, but take heart: You can get many of the same benefits with an electric radiant floor heating system, which is much less expensive to install. The kicker is that electric radiant heat isn't nearly as cost-effective as hot water heat in the long run, and it isn't practical as a whole-house heating solution. However, if you're just interested in making one or two rooms more comfortable, electric radiant floor heat may be just what you're looking for.

Like the PEX pipes for a hydronic system, the heating cable for an electric radiant floor system can go underneath the subfloor or between the subfloor and the floor covering. Most homeowners opt for the latter because putting the cable above the subfloor instead of underneath it makes the heat more readily available, and you end up using less electricity.

Although electric floor heating is easier and less costly to install than hydronic heating — installation can even be a DIY project — it's still worth a second thought before you go ahead and do it. Unlike a hydronic system, an electric system is intended more for warming the floor than heating the entire room, and it works best in rooms that already have forced-air systems or some other type of heating but are still a little too cold. It will make your feet feel more cozy, and it may raise the air temperature in a particular room by a few degrees, which may be exactly what you want.

Fewer components are needed for an electric radiant heat system than for a hydronic one, and they are easier to install. Because the power source is electricity, you can simply wire the system to an electrical circuit, and in some cases, all you need to do is plug it into a GFCI receptacle. That's much easier than installing a boiler and circulation pump. An electric radiant floor heating system has only three components: heating cable, a temperature sensor and a floor-heating thermostat.

Instead of PEX tubing to carry water, an electric radiant heat system uses electrical cables that function like the resistive elements in electric space heaters, although they don't get nearly as hot. They consume from 6 to 12 watts per square foot, which amounts to 600 to 1,200 watts for a 100-square-foot room. The cables can be powered by either a 120- or 240-volt electrical circuit; 120 volts works better for smaller floors, whereas 240 volts is preferable for larger ones. A 240-volt system draws less current (amperage, measured in amps) than a 120-volt system to achieve the same power level, and that makes a difference to the line thermostat that controls the system, which can typically handle a maximum current of 15 amps.

Radiant floor cable can be purchased on a spool, allowing the installer to unwind it and place it as needed on the subfloor. This arrangement works best for rooms with irregular shapes, but for square or rectangular rooms, cable that has already been attached to plastic mesh to form mats is more efficient. Mats are typically divided into discrete sections that can be unfolded in more than one orientation, allowing a single mat system to work in a variety of situations. You can cut mats as needed to fit around obstructions, but you can't cut the cables.

Unlike a hydronic radiant floor heat system, an electric one offers easy installation that can generally be a DIY project provided all the electrical circuitry to power it is in place. Smaller systems that draw less than 12 amps can often be connected to existing circuits, but larger systems — especially those that operate at 240 volts — may need their own dedicated circuits and circuit breakers. Any homeowner planning a new electrical floor heating system who is in doubt about the electrical requirements should consult with an electrician and have any necessary work performed by that person.

After establishing how the system will receive power and cleaning the subfloor (removing the existing floor covering if necessary), installing the heating elements is simple. When using mats such as those supplied by SunTouch, you deploy them to cover as much of the subfloor as possible, cutting the mesh as needed to form corners or create side-by-side runs and attaching the mesh to the subfloor with hot glue or staples. When installing cable from a spool, you wind it back and forth across the floor, maintaining the spacing recommended by the manufacturer and using hot glue to secure the cable to the floor. Staples should not be used with unmeshed cable because of the danger of piercing through the cable sheathing, which would cut power to the entire cable system.

Once the cable is secured, the installer typically covers it with thinset mortar, or when a perfectly flat surface is preferred for installation of ceramic tile or laminate flooring, floor-leveling compound. Thinset has to be troweled flat, but leveling compound is a liquid when you apply it, and it flows out to seek its own level. Either way, the entire cable system along with the temperature sensor supplied with the heating system has to be completely encapsulated, and when the compound sets and dries, you lay the flooring directly over it and hook up the heating elements. That's all there is to it.

The cost for electric floor mats designed to be installed under flooring vary, but as examples, a 10-square-foot SunTouch mat costs $137, while a 90-square-foot LuxHeat mat costs about $500. Once the mat is installed, operating costs depend on the local rate for electricity, which can vary from 12 cents per kilowatt-hour in Colorado (which is close to the national average) to 21 cents in California. If you pay the Colorado rate, it will cost about 50 cents to provide heating for a two-hour period in the morning and a two-hour period in the evening, or about $15 per month. In California, you'll pay 84 cents per day, or about $25 per month.

In general, floor coverings for radiant floor heat should have high thermal absorptivity and transmissivity. Ceramic and stone tiles are probably the best choice, followed by polished concrete or cementitious composite, such as terrazzo. Carpeting is a less than ideal choice, but if the building is well-insulated and doesn't lose much heat through the subfloor, carpeting with a maximum pile height of 3/4 inch installed on a 1/4-inch pad is acceptable. Carpeting will feel especially comfortable under the feet when it is warmed, but it won't radiate much heat into the room.

Some types of flooring can shrink and show gaps when subjected to the constant heat of a radiant floor heating system. Vinyl tile, laminate and hardwood flooring are particularly vulnerable, but potential for damage depends on the temperature of the floor. On older, poorly sealed homes, it's often necessary to maintain the floor at a temperature of 90 degrees for comfort, and that's high enough to cause curling, gapping and shrinking. In newer homes that are well-sealed and lose little heat, temperatures of 80 degrees or less may be comfortable, and that's the typical manufacturer's upper limit for most wood and vinyl flooring products, so it would be safe to use them.

When choosing a wood flooring product for installation of a radiant floor,. you'll want to limit your choices to engineered products because solid hardwood is more vulnerable to warping and cupping. It stands to reason that any product you choose should come in either snap-together planks that create floating floors or in planks that can be glued down. You can't drive nails into the floor without risking damage to the heating cable.

Radiant heat systems provide comfortable heat that warms from the ground up, and that in itself is a good reason to consider one, but hydronic heat systems can be very expensive to install. Electric radiant heat, on the other hand, costs far less up front, and it offers these benefits among others:

• ​Maintenance-free:​ Once the system is installed and the flooring has been laid, an electric radiant floor heating system requires no other maintenance. There are no filters or ducts to clean and no machinery to monitor.

• ​No noise:​ Unlike a traditional HVAC heating system, there's no blower, compressor or other machinery running when the system is on.

• ​Uniform heating:​ All areas of the floor feel equally warm. Compare this to electric baseboard heaters or room space heaters, which warm the space around them more than the space on the other side of the room.

• ​Better air quality:​ Unlike an HVAC heating system, a radiant floor system won't broadcast allergens and other impurities through the air.

• ​Energy efficient:​ Electric floor heat is more efficient than using baseboard heaters or electric space heaters. A system running at 12 watts per square foot consumes 1,200 watts in a 100-square-foot room, whereas any other type of electric heater typically consumes 1,500 watts while producing less uniform heating. When used with a programmable thermostat, an electric floor heating system is even more efficient. Because the flooring continues to radiate heat after the power switches off, the thermostat can be programmed to cut power more frequently than would be possible with a baseboard or space heater, and if the thermostat is Wi-Fi enabled, you can do this remotely.

Some of the drawbacks of electric radiant heat include:

• ​New floor covering:​ Although installation is easy enough to DIY, it does require removal of the existing floor covering and installation of a new one. The best time to install electric floor heat is during new construction, but if you do it on an existing floor, you have to be prepared for the extra costs and labor involved with changing the floor covering. You can get around this by simply laying an electric floor heating mat — which either looks like carpet or is intended to go under a carpet — on the parts of the floor on which you walk.

• ​Increase in floor height:​ Installing heating cables under the floor will raise the level by a small but significant amount — up to about 1/2 inch —which could create awkward transitions at doorways and require the doors and door trim to be undercut.

• ​Not energy efficient:​ Although a radiant floor system seems efficient when compared to other types of electric heaters, the fact is that electric heat is the most expensive kind of home heating. Electric radiant floor heat is less energy efficient than hydronic floor heat, and the efficiency rating goes down even more when you consider that electric floor heat usually has to be used in conjunction with another heat source for complete room heating.