Synopsis: Radiant-floor heating systems are arguably the most comfortable and energy-efficient choice for home heating. This articles details a system where the water pipes are routed through plywood panels rather than concrete, making the whole thing easier to install. Sidebars cover the pros and cons of radiant heat, an overview of other systems, and a discussion of flooring choices.

When I answer the alarm clock in the dead of winter, I set my bare feet on the hardwood floor to get an idea of the temperature outside. If the floor is warm, I know it’s cold out. My radiant floor heating system answers the chill of a New England winter by putting the warmth where it counts: right under my feet. After four Rhode Island winters, I can say that this type of heating system is the most comfortable I’ve ever experienced.

A hydronic radiant-floor heating system works by pumping heated water through cross linked polyethylene (PEX) tubes that run under the floor. The floor then functions as a huge radiator, emitting an even, low temperature heat.

Thanks to some simple, well designed components, the new “dry” radiant-floor heating systems can be installed with basic carpentry skills. The system that I use doesn’t require any special framing and adds only 1⁄2 in. to the floor height.

A heating contractor designs the system

Even for a single-room addition like the one featured here, it’s important to have an experienced heating contractor design the radiant-heating system. The contractor calculates the heat loss for the room(s) accounting for climate, room size, insulation values, glazing area, and the type of finish flooring to be installed.

Using specialized software, the system designer selects the diameter (usually between 5⁄16 in. and 5⁄8 in.) and spacing (usually between 6 in. and 12 in.) of tubing, the length of the tubing runs, and the water temperature and pumping requirements. Finally, the contractor recommends the control components used for monitoring and regulating the heating system.

Multiple tubes mean even heat

If one long, continuous length of PEX tubing was used for the system, it wouldn’t work well. The drop in water temperature from the beginning to the end of the tube would render the last part of the system almost ineffective, and the floor would not warm evenly. To prevent this heat loss, radiant floor heating systems rely on multiple loops, or runs, of tubing. Each run begins at a supply manifold and ends at a return manifold. To prevent the water temperature at the return manifold from dropping much below the supply temperature, each run of tube usually is limited to around 250 ft.

Your heating contractor can help you to locate the manifolds so that the runs are kept to minimum lengths and so that they cover distances that are relatively uniform.

Grooved panels install quickly

Once the manifold location is established, I lay out the path of the tubing. On this project, I used Wirsbo Quik Trak. (Similar panels are made by RTI Piping Systems, Stadler-Viega, and Warmboard.) The straight-run panels measure 7 in. wide by 48 in. long with a channel in the center to accept 5⁄16-in. PEX tubing. Each panel is backed with a thin layer of aluminum that helps to disperse the heat and reflect it upward.

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