Radiant heat isn't just for concrete slabs.

In the beginning, there were concrete and thin slab installations, or "wet" radiant systems, where tubing was covered by concrete, light concrete, drypack or gypsum underlayment. Then came the staple-up applications where tubing was attached to the underside of existing subfloor. Both types of radiant in-floor installation were time-consuming and sometimes difficult to install.

Contractors looking for an alternative to these types of installation now have radiant for above the subfloor - easy to install, quick heat response time, lower profile, clear view of tubing as finished floor is installed, and perfect for retrofit and new construction projects.

"More and more contractors are looking for above-the-floor options," says Mark Fries, sales and engineering manager at Watts Radiant. "They don't want to mess with a wet system, and often it's not possible to get under the floor to install tubing, especially if it is a slab."

With more people interested in radiant floor heat, the market in North America is increasing, says Bill Johansen, department manager for REHAU's heating and plumbing group. The reluctance of some builders and mechanical contractors to the poured concrete method has made subfloor installations more popular.

Radiant contractors now have more installation options, but none is more labor-saving than the subfloor panel products on the market today.

There's Nothing To It

With subfloor panels, there is little preparation - just make sure the floor is dry and level. And no special tools are needed.

  • REHAU has one of the newest products on the market, the RAUPANEL[TM] System. It consists of aluminum panels, wood return bends and plywood spacers, and has a low profile of 5/8-inches.

    Each all-aluminum panel is 1/8-inch thick, 6 inches wide and 6 feet long, with grooves to fit 3/8-inch pipe. At the very ends, the aluminum is turned down to form a small "stand." These stands provide support. The end return bends are plywood with curved grooves.

    To install, just lay the panels on the floor so the stands are on the floor. The return bends have a specialized locking mechanism and guide, so the plates just snap into the end pieces. Pipe is snapped into the grooves. REHAU does provide a specialized metal cutting blade for a typical skil saw if a panel needs to be cut, and a deburring tool to take the sharp edge off of a cut.

    "The real difference in this product is that this is not a laminate product," Johansen notes. "The whole panel is a heat conductor itself. Because of the thickness, the shape and the material, it conducts heat quickly and transfers heat off the floor more efficiently."

  • Stadler-Viega is one of the pioneers of this type of system - its Climate Panel[R] System consists of two pieces of 1/2-inch plywood "perforated" with an aluminum back and filler strips with curved grooves. The panels are 7 inches or 10 inches wide and 4 feet long, and have a profile of 1/2 inch.

    Installation is quick; lay the panels out on the subfloor, secure with staples or screws, snap the PEX tubing into place. To install over an existing slab, adhere a plywood layer to the slab and install the Climate Panels on top.

    "The Climate Panel arrives at the jobsite pre-assembled with an aluminum back so that all the contractor has to do is staple or screw it to the subfloor and walk in the Pextron tubing," explains Andy Fiefhaus, vice president and general manager at Stadler-Viega. "With the unfolding 'six-pack' (preAssembled Climate Panels), up to 20 square feet of floor coverage is easily and quickly installed at a time."

  • Quik Trak[TM], Uponor Wirsbo's subfloor product, is the same concept: 7-inch or 10-inch panels attached to aluminum heat transfer sheets on the bottom, Return Traks with grooves for the ends.

    Panels are screwed to the subfloor, and PEX tubing is easily snapped into the grooves. Even faster installation is achieved with the Quik Pak preassembled system, which covers more ground in one shot.

    "Quik Trak was designed for low-intrusion in the structure," says Jan Andersson, heating brand manager at Uponor Wirsbo. "A gypcrete system would require a 1 1/2-inch or 1 1/4-inch pour, which needs to be accommodated in the structure. With Quik Trak, you only have to accommodate for 1/2 inch using 5/16-inch tubing.

    "Although the tubing is small in diameter, at fairly close spacing it helps even out the temperature. The aluminum emission plate underneath the tubing itself helps spread out the heat evenly."

  • The SubRay system from Watts Radiant comes equipped with the following:
      6-inch wide sleepers (made of Baltic birch plywood);

      radiant tape (applied to the bottom of each radiant "channel");

      header sticks (to hold pipe at each end of a room);

      corner sweeps (to help the PEX tubing make 90 degree turns);

      grippers (to hold PEX tubing where it enters and exits floor);

      C-covers (to protect tubing from nails); and

      aluminum conduction rolls (installed over sleepers to conduct heat more evenly).

    The system comes in two sizes: the 13 mm. version uses 3/8-inch PEX tubing, and the 17 mm. version uses either 3/8-inch Onix tubing or 1/2-inch PEX tubing.

    First the header sticks are installed, then the sleepers and corner sweeps. Next the tubing is placed in the wide channels, and the aluminum conduction roll is applied on top. SubRay uses wide channels instead of tight grooves, permitting easy movement of the tube with no noise.

    "SubRay is extremely stable, durable and easy to work with," Fries says. "It has a more modular design and is versatile for odd-shaped rooms. Also, Watts Radiant doesn't require constant circulation, like some other systems. This potentially reduces the cost of electronic controls for the project."

  • RTI PEX Plumbing Systems has ThermalBoard[TM], which is made up of medium density fiberboard and a thin layer of aluminum glued to the top. The fiberboard is very dense and allows for good heat transfer. There are three different configurations that fit together like a puzzle. The panels have grooves for PEX tubing.

    Just assemble the panels, attach to the subfloor and snap in the 3/8-inch PEX tubing, creating a low profile of 5/8 inch.

    "ThermalBoard was developed with the homeowner, contractor and engineer in mind," explains David Holdorf, engineering manager at RTI. "Not all radiant systems need to be embedded in a concrete or gypsum-based product. Not all projects can handle nor do they warrant the extra weight or height. These products were developed as a result of expanding radiant floor heating systems to incorporate into the entire house."

  • Thermal Track[TM] from Zurn PEX Plumbing and Radiant Heating Systems is another product made of medium density fiberboard and an aluminum top layer (Thermal Track Warmcoat). Thermal Track also comes in three panel sizes. To install, cut to size and piece in. Then snap in the standard 3/8-inch tubing.

    "It minimizes how high you have to raise the floor to put the radiant heating system in - only 5/8-inch," says Patrick Sauer, Zurn's vice president of sales marketing. "And the aluminum layer on top maximizes response time - it heats up much quicker than a concrete pour or staple-up."

  • HeatLink's newest product, available this summer, is the Dry-Above[TM] system - consisting of a sleeper, a plate, pipe and support material that can be found at your local lumberyard. Installation is easy because standard components are used, including the heat transfer plates. The EndBend component allows for transition on the loop ends.

    "One of the great advantages in above-subfloor installations is the option of multiple pipe spacing," notes Manfred Schmidt, director of the HeatLink Group. "The Dry-Above system can generate outputs from 20 to 30 Btu/hr./sq. ft., depending on pipe spacing and floor coverings chosen. Floor surface temperatures are maintained at a maximum of 85 degrees F."

    Another product out in the market is Warmboard[R] (from the company of the same name), a tongue-and-groove plywood structural subfloor panel with channels for tubing, and covered with aluminum. It is manufactured from sustainable and recycled resources, and is installed as a standard subfloor.

    Advantages Over Wet Systems

    There are many advantages to using above-the-subfloor systems for the contractor, the builder and the homeowner. "From the perspective of the contractor, he can control more of the process himself," Johansen says. "With a wet system, he might have to get a specialized concrete installer or a specialized gypsum cement installer. With this system, he can install the whole system and actually sell the product, not just mark up the other guy's subcontracted material."

    For the builder, dry radiant means a condensed building period, he says. He doesn't have to worry about the wet material in the building or wait for the gypcrete or concrete to dry. And he won't have to clear the building of other trades for an entire day while concrete is being poured.

    He adds that the homeowner is assured he is getting a flat floor, not wavy or bumpy. And because the response time is much quicker, it makes heating during the shoulder months of the year - spring and fall - much easier.

    There's also the perception of the installation from the homeowner's point of view. "Even though radiant tubing has been embedded in concrete flooring systems for many years and accounts for a very large percentage of radiant floor heating installations, some homeowners still don't like the fact of placing the tubing in concrete to never access it again without major demolition," Holdorf notes.

    Another plus for subfloor systems is it's ideally suited for retrofit applications. "Dry systems in general are much easier to retrofit because they don't involve digging up concrete to place the tubing," Andersson notes.

    "Dry systems are often the only alternative for areas of the country where it is difficult or too expensive to get a concrete installer to do the job," Fries says. "Also, many retrofit jobs are just too small for a wet system."

    And, with subfloor radiant systems there are no costly framing adaptations required to support the weight of concrete, Fiefhaus adds.

    But its versatility allows for use in new construction and with all types of flooring materials. Thin-set tile can be applied with cement board over the plates/panels, carpeted floors can be installed by covering the radiant subfloor with plywood, and hardwood flooring can be applied directly on top, says Schmidt.

    Because these systems have a lower mass, they react quicker to water temperature changes, Andersson says. They also use lower water temperatures, and react to increased heat load in the room, dissipating the heat quicker.

    "There are a lot of inherent differences between 'wet' and 'dry' radiant systems," Holdorf says. "One is not necessarily better than the other. Mostly it has to deal with making the radiant system fit the construction of the house, not making the house fit the radiant system."