We've jsut been having some debates about slab UFH strategies on the relevant forum, but I wanted to do some sanity checks without getting into over-specified 2D or 3D heat flow equations, which I then need to modle.  Some of you have probably come across this type of graphic (source BuildingPhysics.com):   (BTW the reason for the alternating hot and not-so-hot pipes is that if you think about it, this is house UFH loops are laid, using the double-back technique.)  This also looks