Radiant Floor Warming

   Getting a stone floor to a bearable temperature in winter used to be the province of the rich, along with other niceties like heated towel racks and a car phone. Like other luxuries, however, a heated stone floor is becoming more of a commodity upsell than an extravagance.
   Today, practicality and comfort are coming together with the advent of cost-effective radiant floor systems. Various vendors are making the heating units easy to install – and all of them are warm to working with stone.
  
WATER OR ELECTRIC?
   Getting toasty underfoot may not be quite the norm but the idea of floor warming is on the upswing. Vance Sherwood, of the Loveland, Colo.-based Radiant Panel Association, says radiant heat consists of three percent to five percent of today’s heating market, but grew 13 percent in the past year – and continues to gain in popularity.
   Radiant heat is trendy these days, says Dan Chiles, vice president for marketing of Watts Radiant, a Springfield, Mo.-based manufacturer.
   “There are two reasons for that,” he says. “It’s predominant in bathrooms and kitchens. That’s a woman’s world where they have the decision-making authority. But radiant heat is cheap to operate, so now you’re in the male world. It’s practical.”
   Unlike convection or forced air heating, radiant heat only warms cold objects, not the air. The first thing to be heated is the floor; after that, radiant heat can warm the walls, furniture and other items in the house. Because of that capability, it can be used as the only heat source in a well-insulated household.
   “Radiant is a broadcasting system,” Chiles explains. “Like light, if it’s at the surface of the floor it broadcasts at the speed of light and then strikes objects in the room and scatters just like light. It’s like being out on a warm spring day and you find black rocks; you can nestle in those hot rocks and feel wonderful.”
   The two sources of radiant heat – hydronic and electric – offer different solutions for different environments.  Both are capable of heating a floor; the speed at which the heat is absorbed and subsequently held depends on the density of the covering material, whether it’s stone, carpet or ceramic tile.
   Stone holds an advantage in floor warming with the ability to absorb and distribute heat evenly, says Tracy Stanger, president of Salt Lake City-based Warmzone.
   “Some stones, like a dense marble, will have a slower reaction time,” he says, “but once heated, it retains it, giving off heat much more evenly over a longer period of time.”
   Whether using a water-based or electric-wire system, the floor will provide the same degree of heat. The cost of each system, however, varies.
   A hydronic system is most economical when used in a large space due to its high set-up costs; it’s also more-difficult to maintain or repair.
   Institutions such as churches, shopping malls, factories and schools benefit from the large-scale savings with the system. Homeowners, who may only desire a warm kitchen or bathroom floor, don’t.
   Using a hydronic system in an average home is overkill, Stanger says. Approximately 1000 ft² of total area to be heated is the breaking point between electronic and hydronic systems.
   “In hydronics, some of the products are cheap, but when you do it on a small scale, the economics of scale aren’t working for you, so you have to get into big areas to spread the cost out,” Stanger says.
   When installing a hydronic system, it’s ideal to put the water tubes in when the home or institution is being built; the tubes are laid directly in the reinforcing wire mesh or welded wire fabric of the concrete slab as it’s poured. To install them after the original slab is finished requires more concrete and wire mesh, thus raising the height of a pre-existing floor.
   Then there’s access to water. Water needs to be pre-heated before running through the system, requiring some kind of auxiliary source (anything from an electric boiler to solar-powered heat.). And the warm water also requires a pump to keep it circulating throughout the system.
   “It’s high-maintenance and complex,” Stanger says. For example, if there’s a problem after installation – i.e., a leak in the tubes – the floor has to be removed to find it.
   Since water takes longer to heat than the wires or cables that run through an electric system, the radiant heating contractor sets the temperature of the water at the time of installation, based on the environment and the customer’s requirements, and that’s where the temperature stays. The heat is programmed to begin warming the water, say, an hour before the homeowner wakes in the morning.
   On a smaller scale, including million-dollar custom homes, an electric radiant heat system is easily installed in both new construction and pre-existing environments.
   Electric radiant heating systems can be put in as cables and placed around objects, or as a mat containing pre-spaced cables. Whichever system is chosen, each must have a coat of thin set or mastic applied over it.
   “The cable needs something to heat sink it or pull the heat away from it and distribute it evenly,” Stanger says.
   Free-form cable can be wound around toilets or other odd-shaped appliances, while the mat cannot. However, the mat is convenient and easy to handle for initial installations.
   The heat cables are stapled to the floor joists, or tacked to the sub-floor. If they are installed in a room over a lower level, such as a basement or crawlspace, it’s recommended to insulate below the cables so the heat will not disperse below, but rather stay in the stone floor for which it was intended.
  
SAFE TO SHOWER ON
   Both systems are protected by GFCI (ground fault circuit interrupter) and fully grounded so danger of electric shock is practically non-existent, Watts Radiant’s Chiles says. Some systems are safe enough to be installed in shower floors.
   Electric systems are installed along with a thermostat enabling the customer to set and change temperatures when the environment calls for it.
   The key to installing a reliable electric system, according to Chiles, is to monitor the cables as they’re being installed, with an ohmmeter, assuring there’s a constant current.
   “Some stone masons using mud and a trowel may clean the mud off the trowel by banging it on the floor,” he says, “and that could damage the cables.”
   Once installed, an electrician should be called in to finish the final connection.
   Warm or cold air temperatures and humidity don’t affect the radiant-heat systems. Chiles, whose company manufactures both hydronic and electric systems, says heating cold stone floors originated in Europe and he’s seen them installed all over the world, including the bitter cold of the Dakotas to the balmy Caribbean. Cost is relative to the amount of stone requiring warmth.
   Warmzone’s Stanger says installation of an electric system, aside from flooring materials, runs about $5 to $7 a square foot, retail, including the thermostats.
   Pam Dirks of Spencer Tile owns and operates a flooring installation company that supplies custom homes along the shores of the lakes near her home base of Spencer, Iowa. She says that while most of her customers can afford the heating systems as a luxury item, the real reason they buy it is for the practicality of heating their stone floors.
   “It’s so cold here in the winter,” she says, “you either heat the stone floor, or you don’t put it in.”
   Spencer Tile recently priced a 528 ft² area at more than $5,000 for installation of the mat heating system. But Dirks says if a customer can afford to put stone in their home, they can usually afford to heat it, too.

This article first appeared in the January 2005 print edition of Stone Business. ©2005 Western Business Media Inc.