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i am not exactly a newbie for radiant systems. Been installing them for more than thirty years and used to be a regular on "The Wall". I've always avoided heating slabs over 5", figuring the problems of lag and overshoot/undershoot would be too great. Coming back to the question now. I have a customer who wants to install radiant heating in a 12" slab. Underslab and perimeter insulation are a given. I'm thinking that if I can keep the tube about 2" below the surface that will help a lot. Also, it seems to me that keeping water temperatures down using outdoor reset with the "boost" feature on the boiler may minimize overshoot/undershoot while allowing somewhat reasonable warm-up times from cold start (due to "boost" feature). I would welcome your thoughts.