Route channels in foam for pex-al-pex?

Gordan

Background: low-mass radiant ceilings, modified "Siegenthaler special" - 12" o.c., thin plates adhered (on one side) to 3/4" polyisocyanurate which is in turn adhered to existing ceiling. Furring strips between runs of insulation/tubing, for ease of drywall fastening. (This is on top of a plaster ceiling, so I'd need really long screws to fasten drywall to framing if I didn't screw/glue furring strips.) 1/2" pex-al-pex with 120 max supply - should only expand 1.2" per 100'.



I could just use two 4 7/8" strips of insulation, one on each side of the tubing, butted to a furring strip, leaving a 3/4" channel in the middle, or I could route a 3/4" wide, 5/8" deep channel with a core box router bit. I'm leaning toward the latter because it would allow me to just alternate furring strips and insulation, as opposed to installing furring strips first, then the insulation, all the while worrying about the channel in the middle. It would also allow me to adhere plates to the iso board while on the ground, rather than fussing with them overhead. I'd also like to route return bends into the iso board. Am I asking for noise trouble? Am I asking for installation trouble?

NRT_Rob

why glue?

why not just staple the plates to the furring strips?

Gordan

Less back-side loss

Perhaps slightly lower probability of the drywall hanging crew driving a screw through the tubing.