Q. We just got a job for a concrete floor with a radiant heating system. What do I need to know to get this to come out right?
A. Concrete is the perfect material for radiant floor heating systems. Because of its thermal mass, concrete stores heat and releases it when the temperature changes inside a building. Nationally, radiant floor heating systems represent only about 5% of home heating systems, but its popularity is growing, and in many locations it is becoming the preferred method.
Tubing is one of the most important parts of the system and PEX and PEX-Aluminum-PEX (commonly called PEX-AL-PEX) are the materials of choice. PEX-AL-PEX has the advantage of providing a 100%-oxygen barrier and holding its shape better when placed.
For full-depth concrete applications, Robert Bean, owner of HealthyHeating.com, Calgary, Alberta, Canada, stresses the importance of installing a vapor barrier below the concrete slab, being careful to seal it against the foundation walls. Insulation is the next step—high-density rigid foam commonly is used. Rebars or welded-wire fabric are positioned atop the insulation and the tubing often is attached to the steel. If you use WWF, 6x6 to 10x10 is good—it's better to use flat sheets than rolls. The tubing should be kept 6 inches away from walls and have at least 2 inches of concrete cover.
There isn't anything unusual about placing concrete for radiant floors except that workers must be careful working around the tubing to avoid denting, cutting, or crimping it. Care must be taken with shoveling and pulling concrete into position, and equipment must never be dragged across the tubing.
Multizoned radiant floor systems for midsized homes can be twice the cost of a basic single zoned forced air system. But in larger homes, with longer forced air duct runs, the costs are comparable and can even be less. Owners, however, can save 20% to 30% of their heating bill compared with forced air systems.