Hi everyone glad I found this forum. I have read a good amount of posts with good links and info. Ok I had question.

I am in the process of trying to price out a installing a radiant heating system for our place. I will be doing all the labor so this will be primarily a DIY project. I have read in several places that there needs to be a thermal break over a concrete slab and that the slab must have insulation on its outer walls and below.

The house we are working on is a multi-level split. The dining room, kitchen, and living room are on the first floor and they are on a non insulated poured slab with an outer ring of cinder blocks. (House was built in the 60's and there is no rigid foam on the bottom or in between the cinder blocks and the poured slab. Only thing that I did notice is fiberboard in between the slab which is used an expansion joint.

Originally my plan was to get 3/4" plywood and route my pex tubing channels and then install 3/4" oak wood flooring above. So I was hoping to get some feedback as to whether this would function at all. Most of the articles I have now read say that without insulation and without a thermal break the heating system would be very slow. Wouldn't the plywood function as a thermal break from the concrete? 

You must start by insulated the perimeter, (dig, insulate and back fill). You must also insulate on top of the slab. Roth, Rehau, Uponor and Viega all make viable "sandwich" radiant systems ready to go.