OK. Thanks.

By the way, the DITRA application is right out of Warmboard recommendation. They say that it may not be approved by DITRA but have hundreds of installations that work well installed this way. I am also seeing some  flooring guys go this way.

warmboard is 1-1/8" douglas fir plywood.

Radiant Shield is rigid foam.

That is not a comparable situation for supporting a tile finish floor, IMHO. then again, I haven't computed the compression issues involved. but I sure wouldn't do it.

I checked the LP Tech Shield specification to verify. It is OSB. I understand there are concerns about OSB under stone tile so I may have to look at this more carefully.
I believe DITRA works in this situation.

Also see http://www.tecspecialty.com/content/newSolutions.aspx

if I got the wrong product I apologize; I thought the radiant shield was an insulation product. then you are one step from a sandwich already. Instead of wasting money on a reflective layer that won't help, put in some plates, use PEX-AL-PEX and you're ready to roll.

Thanks. I appreciate all the comments.