Further, depending on the size of the circuit feeding your existing floor warming system and how much it is drawing from it and how much more you add below, you MAY be able to have them both on the same circuit so that the existing GFI tstat runs them both.
The suggested installation/insulation is as follows:
Staple the Calorique element 1" down from the plywood subfloor and make your connections, then staple a reflective insulation face up 2" down from the Calorique film element and, if you have the room, add fiberglass insulation below the reflective. This will give you the best design to get the maximum use of the retro-fit radiant from below.
Thanks all. Ripping out the tiles and mud job isn't an option - unless I want the wife to leave me=)
I like the idea of filling in the cold spots with electric radiant from below (the existing floor heat is on its own 20a circuit so I do have the room there). My concern would be -will the staple up radiant make its way up through a 1" mud job and another 1/2" or so of tile and thinset? Even if it did warm p the floor In those spots, i would have to supplement the floor heat with a baseboard radiator.
I'm not opposed at all to putting in hydronic radiant under the entire floor. I was thinking of installing the hydronic radiant under the subfloor using those aluminum plates, then insulating under all that, and then installing a runtal baseboard heater in the room as well. I have a plumber coming tomorrow to look at everything. After my first experience I would like to try to figure out the btus needed to heat the room so I can size the radiator appropriately.