Does a porcelain tile floor need a moisture barrier?

Hello! This may be a silly question, but we're new Eichler homeowners in Orange County doing a little work on the house and we want to make sure we get it right. The Eichler we own currently has carpet in all the living areas and we've chosen to replace that with porcelain tile. We chose this because our radiant heating system still works and we know that porcelain tile will conduct heat well, it will be fairly easy to clean, and if we have any issues with the heating system like leaks, fixing them won't be as difficult as with some other flooring materials (the system has sprung two leaks in the past which have since been fixed). Now, during a brief period when we were considering installing hardwood, it was suggested to us that we use a moisture barrier like RedGard to help prevent the wood from cupping or buckling. My question is, now that we've finally decided to go with porcelain tile, do we still need to worry about moisture issues at all? Or are we in the clear and in a position to save a few bucks by not putting in a moisture barrier? Thanks!
Tiffany