Winter is here, and with it comes the seasonal rise in heating bills. One great option to warm a room efficiently and cost-effectively is through the use of electric radiant floor heating. While the product – whether a wire, mat or film – is designed to install easily, several considerations must be made to ensure a long-lasting and trouble-free installation.

Eric Kurtz, Bostik market manager, hardwood installation systems, said while his company’s HeatStep mat and wire systems can be used under tile, the company is focusing on its use under hardwood floors. “We’re marketing very heavily toward hardwood. It has to be encapsulated in a cementitious layer, and make sure to follow the recommendations of the hardwood flooring manufacturer,” he said. “Most manufacturers will specify that the heat not go past 82 to 84 degrees Fahrenheit.”

Ed Gilmartin, national sales manager of Calorique LLC, said his company’s range of radiant floor warming products can be used under most floor coverings. “The only time you need to be careful is glue-down. You have to make sure the glue does not soften and lose adhesion due to heat.”

He noted his company has been working with wood and laminate manufacturers to test the thin, lightweight film product. “We got the wood flooring manufacturers’ recommendations and tuned our ink mix to meet them. They were: Max temp of 85 degrees Fahrenheit and an increase of no more than 10 degrees per hour. The new product is six watts per sq. ft. and is with 10 laminate manufacturers for testing.”

Calorique’s Perfectly Warm tile product is designed for wet areas like bathrooms. However, Gilmartin warns, “We don’t suggest using it in the shower floor. We have some small requests for that but believe it does not make sense right now to develop a product. That may change if we see a market for it.”

Monica Irgens, Electro Plastics president, said there is a wide array of electric radiant heating systems available, including wires on a spool, wires in a mesh or mat, thin-film carbon printed heaters and self-regulating PTC semi-conductive polymer elements. “Some heating products can be used under most floor coverings, and others are limited to certain floors. Installers have to carefully read each manufacturer’s installation manual and recommendations.”

For hardwood, which is sensitive to changes in temperature and humidity, “it is very important to install a heating system that maintains an even, low temperature over the whole floor surface,” she said. For wet areas such as bathrooms, “installations of electric radiant heat are only approved if those areas are properly protected and maintained dry, using for example a waterproofing membrane.”

She added that selecting the proper R-value for products is important. “The R-values should be higher under versus over the heating elements, ideally 4:1. This may not always be possible; it is more important that there are no air gaps. Also, choose a floor covering that has a lower R-value, ideally not going over R-2.”

According to Romy Sheynis, product marketing manager for EGS Electrical Group which includes the EasyHeat brand, his company’s electric heating mats and cables can be installed under tile, stone, glass mosaic, engineered woods and laminates (except nail-down) and terrazzo.

“Our products will operate just as well with mortar as with self-leveling underlayment, provided the installation instructions are fully followed,” he noted. The products can also be installed in wet areas and under tiled showers. He lays out the basic installation instructions.

“Lay the mat or cable on the floor first, then covering with a scratch coat of cement-based underlayment. The waterproofing membrane is then installed on top of the scratch coat and the flooring completed in the usual manner. Consult with the local electrical authority to make sure that wet applications are allowed.”

Whenever installing electric heating under hardwood, Sheynis recommends keeping a humidifier or dehumidifier in the room. “Since hardwood floors are sensitive to humidity, it is recommended to have the humidity levels under control.”

Sheynis added that his company stipulates in its installation instructions that thermal insulation of the space below the floor to be heated is optional. “However, it is required that insulation be installed where the temperature of the underlying surface is expected to be less than 50 degrees Fahrenheit. This will reduce energy consumption and improve the performance of your electric radiant system.”

Isabelle Marcil, communications coordinator for Flextherm, has a simple rule of thumb. “For heating areas smaller than 100 sq. ft., you can use either a 120v or 240v cable, while it is cheaper to use a 240v system in rooms larger than 100 sq. ft.”

She added, “It is important to know that a 120v system will not heat less than a 240v system. The cost to run both systems with the same output wattage will also be the same.” The difference is that running a 240v system will draw half the amperage of a 120v system for the same coverage area. “Using one long 240v cable (for a larger area) would cost less than running two shorter 120v cables in the same room,” Marcil noted.

When installing the product, customers can use either a polymer-modified self-leveling underlayment or polymer-modified mortar. If working with a moisture membrane, “always check that the cable can be in direct contact with the membrane. If the membrane has to be installed over the embedded cable, make sure it does not offer any insulation capacities. Never use any rubberized or cork base membrane over the cable.”

Marcil offered these tips for proper site conditions: “Always keep the floor clean, avoid having unnecessary circulation in the room during and after the system’s installation, and between installing the cable and laying the floor covering, the cable should be protected with cardboard or a similar soft material.”

Ken Barnum, Laticrete product manager, said while the typical radiant heating installation goes under tile and stone because “they are the most noticeably cold to the touch,” laminate and floating floor heating systems are also making inroads. “We find that installing floor warming products, whether mat or wire systems, in a cementitious bed provides the greatest level of warmth and control. Cementitious systems allow heat to be transferred easily to the finished floor covering.”

He stressed the importance of following all manufacturers’ instructions. “Continued monitoring of the system using a fault indicator or an Ohm meter can alleviate larger problems later in the installation. Care and understanding should be given to moisture problems, proper preparation, using licensed electricians when required and having a thorough knowledge of how the systems are designed to operate.”

MP Global Products recently launched the QuietWarmth Film radiant heating system and QuietWarmth Fiber underlayment that adds an R-Value of 0.50 to the floor assembly, according to the company. Duane Reimer, technical director, said QuietWarmth Film does not require any additional adhesives or compounds to install.

“We do not need a self-leveler or thin-set to install under floating wood surfaces. Simply make sure there are no items on the subfloor that will pierce the heat film, lay the film and install the floating floor. For tile installs, you must clean the subfloor, apply primer, then peel and stick the mat to the subfloor. The adhesive on the bottom of the anti-fracture membrane will hold the mat in place.”

He said selecting the right R-value for insulation is simple. “Basically, heat goes to cold. As long as the R-value under the heat is higher than the R-value of the value, it will heat the floors. The higher the R-value above, the longer it will take to heat the floor covering. For best results, a high R-value below will direct the heat only where you want it and will result in better energy efficiency.”

Wally Lo, Nuheat product manager, noted, “We suggest keeping the total R-value of the material on top of the Nuheat product under 1.5. Your typical ceramic tile has an R-value of 0.25.”

He also said that mats and cables are more durable than most people think. “We tell contractors to avoid walking on them, but contractors walk on them all the time. They just have to make sure nothing gets dropped on the wires, which may cause damage. So in general, it’s a good idea to avoid walking on the mat or cable after it’s been secured to the floor.”

Don Westra Jr, manager of Wayne Tile in Ramsey, N.J., offered several installation tips for radiant heat systems. “Self-leveling products can be used over radiant cable systems, or you can install radiant mat systems over the top of a self-leveled floor. Liquid-applied moisture and crack isolation membranes need to be applied to the substrate prior to the installation of mat heating systems.”

Westra added that when using one of these systems on or below grade, such as in a basement, “it is recommended that an insulating backer board or membrane be installed prior to installing the radiant heat. This step will reduce heat loss into the concrete.”

Scott Rosenbaum, WarmlyYours Radiant manager of technical support and engineering, said electric floor heat is usually placed above moisture membranes, except when installed in a shower. “The final decision about whether or not an electric floor heat system is allowed in a shower or wet area is made by the Authority Having Jurisdiction (AHJ), whether the local code enforcement office or inspector. The AHJ may also recommend the heating wire is placed under a waterproofing membrane.”

Rosenbaum added that when installing under engineered wood “insulating items that can trap heat, such as dog beds, futons, bean bag chairs and heavy air rugs with foam cushions should never be placed over a heated wood floor.”

He also stressed the importance of testing the radiant heating system with a digital ohm meter. “Test it at several points during the installation: Right out of the box before installing, after the rolls have been put in place but before covering them, and after the flooring has been installed. Never cut, shorten or lengthen the heating wire.”

To avoid damaging the product, “Minimize foot traffic over the rolls, do not wear steel-toed boots when installing the roll, and install the system wire-side down as much as possible. Remove any raised imperfections in the subfloor and verify there are no exposed screws or nails present before installing the radiant heat system.”

Mark Eatherton, executive director of Radiant Professionals Alliance (RPA) said the limit of 85 degrees Fahrenheit under hardwood flooring is often misinterpreted. “When the sun is beating down on hardwood through a window, it gets a lot hotter than 85 degrees. The floor can withstand it. So it’s not really a physical limitation of the product. It’s actually a human physiology limitation. If your skin is in contact with a surface temperature over 85 degrees, your core is going to overheat. So you’re going to start sweating. That’s really the only limitation.”

However one aspect that should not be ignored when installing under hardwood is the ambient conditions. “Make sure the wood is as dry as it can possibly be by allowing it to acclimate. You’re going to need to keep that relative humidity constant, because wood wants to do what it does – shrink in the winter.”

He added that when laying out a radiant floor heating system installation, it is important to keep in mind any vanities, cabinets, tubs and other fixtures. “One common mistake is placing radiant heating under a cabinet, where it’s virtually useless.”