Radiant flooring question
Pex is better at primary heat, but requires more initial cost in boilers/pumps, and adds more height to the floor (1-1/4" mudbed).
Electric can keep the floor warm, but usually will not provide primary heat. Slabs should be insulated with a membrane made for tile use, that has an R value (actually, K values are more important in this application...But I digress..)
1. Acoustic Cork
2.Polystyrene ( or other formulas) expanded sheeting/film (easy mat. whisper mat etc.)
3. Poly sandwich backer boards.(Wedi, Easy board, Bonsal pro panel)
Basically, as you go down the list the price goes higher and the insalting values go higher as well.
I wouldnt install a radint system over a slab without it. The loose wire systems are less expensive and more flexible as mentioned, and I like the Warm Wire by Watts Radiant (Suntouch).
Be careful that when you choose components that they are compatible.
SLC cannot go over cork or Polystyrene sheets, but can go over the rigid backer board panels!
Have fun with your project, & let me know if you have any questions!