What depth should the pex be in a concrete slab?

Nyle

We are soon pouring a 2.5-3.5" concrete slab with radiant heat. The concrete installer would like the pex to be wired to the wire lath, and he will lift it as they pour to get it higher into the slab.

The Plumber insists that he can only anchor the pex directly to the wood subfloor.


Should the Pex be closer to the surface as the concrete guy says? Are there special ties to do the wiring? Is my plumber just lazy?

Thanks

johnnyd

Rebar?

FWIW, around here (SE MN), the convention seems to be staple the PEX to the foam insulation, (you are insulating underneath the salb, right?) lay re-bar over, then pour. So that will bring up more controversy with your subs as whether to use re-mesh or re-bar, and it also sounds like your concrete guy and your plumber are not on the same page regarding this install. IMO, if you're pouring a slab, why would you want to put the tubing in the wood sub-floor like your plumber recommends? I mean, both methods can work well, but usually subfloor/slab installs are done over an existing slab that never got tube.

Concrete guys around here are rightfully wary of tubing floating too close to the slab surface and interfering with finishing and control joints.

Terry

MIddle

The Tubes being encased in concrete s/b in the middle of the slab as the slab is your thermal mass
This allows for running lower water temps (slightly) than if stapled to sub floor.

I tie it to the mesh or rebar.

EIN

Unknown

sounds like this is a suspended slab (slab on deck)?

If so, just staple it to the subfloor. Otherwise you increase your risk of heat striping as the tubing gets closer to the surface, and you need a minimum of 1" of concrete over the top of the pipe as well, and your slab sounds like it would be too thin to risk raising it.

All raising it does is maybe, maybe, marginally reduce your response time.

jerry scharf_3

hmmm

Nyle,

There are different ways to do the job. The idea that the plumber can ONLY attach it to the subfloor is silly, it can be done both ways. It's a bit amusing, normally the concrete guys like it at the bottom so it can't float up and get in the way of their floating. Usually the heating guys like it in the middle for slightly better heating.

The big issues, IMO, are keeping the tubing in place during the pour and not crushing the pipe during installation. With a solid subfloor to screw to, the bottom location will give more consistent heating. The tubing is just not going to move or vary in depth. As for the crush protection, being over the rebar seems better than being under it as the concrete guys tromp around. Maybe putting a small plywood block slightly thicker than the tubing next to the tubing where the rebar crosses over would prevent this as well.

I think this is less about heating and more about what's easier for the contractors. If the heating guy can get in before the concrete guys, he has more scheduling flexibility and cleaner working conditions. If the tubing goes in after the rebar, the concrete guy has less to work around and less risk of damaging things.

just my $.02

jerry