A.Hydronic heating contractor Bill Clinton responds: We typically try to keep at least an inch of concrete above our tube. If the slab is 4 inches thick and the mesh is in the middle, a 5/8-inch o.d. tube would have about 1 1/4 inches above it. Pulling mesh up during the pour is by nature somewhat inaccurate, so it’s probably best to err on the side of keeping the mesh low in the slab. I don’t believe the height of the tube in the slab is going to make a significant difference in system performance even if it’s on the bottom — the entire slab will be heated in any case. My advice is to let the concrete contractor have it his way.
One point about laying out the tube: Tie it perpendicular to the wire as much as possible, away from parallel strands of wire. The reinforcing value of the wire depends on concrete bonding all the way around it, so it’s best to keep the tube out of the way.
to read the full article.