I just got my radiant set up 3 weeks ago. Pretty close in sqft as yours, 3200. I have a 5" slab with 1/2" ALPEX 12" OC. Walls have 3" of closed cell, Ceiling has 8-9" of open cell, I used metal for the ceiling. I have 95% efficient 110BTU wall hung fired with propane. The shop heats up quick I...