As universally accepted as 12-inch spacing of radiant slab tubing is, engineers should still ask if situations exist where wider tube spacing is feasible.
Without a doubt, the most common tube spacing used in slab-on-grade radiant floor heating is 12 inches. The fact that the foot is a standard unit of length in the U.S. construction industry surely has a lot to do with its common use in tube spacing. In slabs, this spacing allows the tubing to be easily secured to standard 6-inch x 6-inch welded wire reinforcing mat. It also allows tube spacing to be coordinated with other standard building materials such as 4- x 8-foot sheets of plywood and drywall.