Nuheat is a very good brand for in-floor heating under ceramic.

Use cement backer board or Schuter Ditra, NOT just plywood.

My preference is ditra. Its easier to install, lighter, and overall a much better product for its waterproofing, cleavage, load distribution, and uncoupling properties, but it cost more.

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Floorman67--- I read up on Nuheat and it sounds like the application I would like to go with. I am ripping out old floor to get to deck which I am assuming is plywood not OSB. I would like to layer in this manner: Durarock, Nuheat layer mortared in, ceramic layer using 3/8 trowel. Do I really need the Ditra mat? Or did I misunderstand your response? The floor is going to be thick as it is without Ditra. Also how would you recommend adhering the cement board if the deck is OSB? I can't see thin set sticking to OSB very well. Thanks for your help so far

its either ditra OR durock ... not both.

ditra is supeior to cement board which is why I recommended it.

yes u can use the NuHeat and Durock.

As long as the OSB is in stable condition and is at least 5/8" thick, DuRock Cement Board can go over it as per their DuRock Cement Board Installation Instructions.

Durock should be installed over a bed of troweled thinset mortar and anchored with galvanized or aluminum roofing nails regardless of the type of wood subfloor or engineered wood panel subfloor.

Read the durock isntallation intructions on the link I posted above.

The OSB need to be replaced if it is bad condition.

I feel that plywood is a far superior product than base grade OSB, but some manufacturers approve its use dependent on its thickness.