Domestic water lines in a radiant slab

Jon Poland

I have been searching for information on installing pex domestic water lines in a radiant slab on top of the insulation and wire. Will this adversely affect the temperature of the hot and cold water. I would think with domestic flow rate at 60 psi through a 1/2" pex line and a relatively short run of 30' the cold water from the utility and the hot water from the tank should be within a couple of degrees at the point of use. Have any of you out there had any experience with this?
Thank you

Jamie Hall

I've never been much of a fan of water lines in or under a slab -- not because of the temperature problems; you are right in that after you run the water for a minute or two it will drop or rise to be pretty close to the source -- but because if anything goes wrong with the line at some future point, you have no good choices as to repair.

Gordy

See it done all the time

Zman

It makes sense to insulate the lines otherwise it is not a problem.

Jon Poland

Worried the thickness of the insulation will lead to future cracks in the floor

Jon Poland

I've talked to a fellow contractor that said he heard of a case of the hot water not getting hot enough on a long run?

sonofaplumber

The cold water does come out quite warm for ~2 seconds (15' run) with 1/2" pex. Never really cools off to the 45 deg ground water temp either.

I don't mind it but if the dog could talk I bet he'd tell you he doesn't really like his water bowl luke warm.

If your concerned with it just insulate the cold line.

Zman

I would not run it in the slab. It will exchange heat for sure. Just trench it in the insulation underneath...

hot_rod

usually there is a drain line running to where the water lines are headed. and they are in the gravel below the slab, run the pex water alongside the drain lines.

At the very least below the foam insulation.

If you run them in the slab you end up with lines crossing over one another, and with insulation it is up into the slab too much.

Insulation tends to make them float in the concrete pour also, really fasten them down if you go that route.

Jamie Hall

Gordy said:

See it done all the time

True. So do I. I still don't like it!

KC_Jones

There was someone recently with a thread about this very topic.
http://forum.heatinghelp.com/discussion/154967/takes-too-long-to-get-hot-water#latest

Gordy

Jamie Hall said:

Gordy said:

See it done all the time

True. So do I. I still don't like it!

Jamie I'm not a fan unless there is no other way which is far, and few in between.

If it were me, and no other way I would sleeve the lines so if there is future problems a new one could be pulled, with no fittings buried either, and insulate it. Being it will be pex.

Larry Weingarten

I agree with Gordy! One way is to use PVC electrical conduit to make a chase you can pull insulated line/s through, under the slab. This will likely become plumbing code someday and it makes future repair simple. Thermal performance will be better also.

Yours, Larry

Jean-David Beyer

I have hot and cold water lines in my radiant on grade slab. My house was built in 1950, so the heating and domestic water are all 1/2 inch copper. (Modifications not in the slab are now 3/4 inch copper for the most part.)

I to not much care for it, because the cold water gets too hot in winter and the hot water comes out colder than it needs to mainly in the winter. I have a mixer valve from my indirect and I adjusted it to 125F so that it comes out at 120F at the nearest hot water outlet (my shower).

If you have a choice, do not run your domestic water through the slab.