Heat transfer plate spacing

MoJones

Using Type C For 1/2 inch pex 4ft length what is an acceptable spacing between plates along the same track (not parallel to each other). 

hot_rod

8-9" on center is a common spacing. It really relates to how much heat output you expect from the floor panel.
4"-6" or so for the end to end gap.

Tighter spacing requires lower SWT, provides quicker ramp up, and more consistent floor temperature.

Cost factor needs to be considered also, more tube, more plates vs benefit.