In Second-Floor Bathrooms and Bedrooms
Retrofitting radiant on a second floor, where the comfort of warm bathroom tiles or wood flooring under bare feet is a treat, can be trickier. Rarely is there access to second-floor joists from below, so the tubing must go in from above. This could add from ½ inch to 1¼ inches to the floor grade, says Richard, requiring adjustments, such as raising or cutting down doors. (These limitations also apply to a first floor with no basement. So in a kitchen, for example, you must be sure that raising the floor doesn't pin a dishwasher into place.)

Fortunately there are products—Uponor's Quik Trak, Viega's Climate Panel, and Rehau's Raupanel are some—that keep the added height below ¾ inch. According to Rehau project manager John Kimball, these panels can go over most any subfloor—planks, plywood, OSB, or even concrete—as long as it's level and in sound condition.

Once the panels are nailed or screwed down, you can cover them with a variety of finish floors. Because tiles give up their heat readily, they're ideal for radiant heat—so a bathroom is a great place for a retrofit. However, a tile floor includes backer board, thinset, and the tile itself, so it will add more height to the room than, say, linoleum, which goes down over ¼-inch plywood, or wood, which can be laid right over the panels (as long as installers don't nail through the tubing).

That said, just about any conventional floor covering will accommodate radiant. For wood floors, Richard recommends hardwoods like oak, ash, or maple. "The narrower the plank, the better," he says. "It keeps expansion and contraction to a minimum." Carpeting will also work, as long as the combined insulating value for the carpet and pad—information carpet dealers or radiant contractors should have—doesn't exceed R-2.5. "If the floor is too well insulated," says Richard, "it's like putting a sweater over a radiator."

Connecting a second-floor radiant system to the heat source is just a matter of finding a way to get the water from the boiler. Basically, wherever PEX tubes can be installed, radiant heat can travel. Richard recommends installing a manifold "in a closet, or tucked into a stud cavity—close to the area being heated." This avoids snaking multiple lengths of tubing down to and back from a distant manifold. Then a single line can supply the water from the boiler to the manifold.
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