pex crossing concrete breaks and pex layouts

[egads74]

First may I too mention GREAT site...

I have read that concrete break cuts are made approximately at 10' x 10' or 12 x 12. The goal is to control the break. Yet I dont seem to see that modeled here to often? What am I missing on this?

Next in reading literature from various pex providers.... and zurn doc from link here... I see mention of dropping the pex down out of the cement at the break cut. Alternative to drop, I also see at a minimum covering the pex (with pipe foam?) at least 2' from the break cut crossing in each direction. Yet I dont seem to see that modeled here? Again, am I missing something on this?

An other concern, it would then seem best to minimize the number of time pex crosses over a break cut in cement. This would reduce the number of dips down as mentioned above or the number of coverings.

I read that concrete does 2 things: get hard and cracks. So if the break occurs then the rebar will hold it all together... I am guessing that the rebar helps prevent the movement of the now broken slabs... so thinking if the slab moved up/down ect... then that would be a potential concern w/ pex going thru. Maybe I am overthinking this... the pex should expand a bit and the cement movement should be minute? And hopefully there should be no leaks. Obviously if it heaves majorly, other issues exist.

I have also read that the pex expands inward when in cement. The cement holds the outside of the tube tight causing the inside diameter to become ever so slightly smaller as the tub expands.

So if it makes sense to minimize the number of break crosses why then are folks just tossing the tube in without concern?

I have also read about tube placement 1/3 way up from the bottom of the slab as best for performance... while they do state tubing can be attached to foam.

I have read about the different patterns when laying pex to address heat loss of walls/ 2 walls / doors and windows. I dont see much increase in number of tubes or tightness of loops at garage doors for example.

I can see the benefit of a tube going out and coming straight back as it has less resistence in pumping verses a tube with 20 turns. Overall though I think one can design with trying to minimize turns or make wide turns.

As far as tightness of loop for 1/2", I kept hearing to be no wider than 9" to avoid cold spots... and be most efficient. Wondering?

I will try to post my pex design layout this evening for feedback good & bad.
thanks

 

[chevelle64]

WOW, I thought I was obsessive . I don't know if I can answer any questions or not, but I can share from my experience of recently installing a system of my own. As far as control joints, mine worked out to be about 8' X 8'. I'm pretty sure most garages on this site that I've seen also use control joints, so I'm a bit confused on that one.

I also was, and still am concerned about the pex being effected by cracks. I don't think there is any way around routing the tubing away from the control joints. As far as dropping the pex below the slab in those areas, I don't really think that's feasible. Mainly because there is usually styrofoam insulation under the slab. You wouldn't want the tubing under the insulation. I'm not really sure if covering the pex with pipe insulation, or anything alse, would actually help if the slab cracks and moves enough.

I attached my tubing to the wire mesh, which sat on the top of my sheets of rigid foam, then I put another layer of wire mesh on top of that. As the slab was poured, the mesh/tubing was lifted to about mid way of the slab. I know that some don't agree with this approach, but that's what I did.

I spaced my tubing tighter around the perimeter, especially in front of the overhead doors. I think others have too. As far as layout, I attempted a spiral pattern. The reason I say attempted, is because it didn't work out exactly as planned. This was the first and only system I've ever installed, so I'm sure that played a part. Between my floor drains, hoist, in-ground lights and plumbing for toilet and sinks, it seemed like I was always avoiding obstacles while laying the tubing. And the tubing is fairly rigid.

The 9" spacing is a bit tight, I went with 12". The 1/2" pex can be bent to a 6" radius. More importantly than the perfect tubing layout is that each run of pex is the same length, and that the correct amount of pex is used. I used Radiantec for all of my supplies, design and overall questions and help.

Sorry I rambled so much, but you started it . Hopefully I answered some of your questions. Don't forget, I am definitely NOT a pro, not do I play one on TV. Good luck.

 

[Ezzie]

I have 3250' of Pex in 2000 sq. ft. of 5" cement floor with control cuts on a roughly 12' x 12' grid pattern. The floor has also got a couple of cracks in an area where i have about 20 passes of tubing going through. So far, no leaks. I'm thinking that the Pex has enough stretch to absorb these minor movements of the concrete and that is why no one has ever expressed any concern about it (at least to me).

 

[antolod]

If your base is stable, you should not have any problems with your tubing at control joints or even in any other area that might crack. At my work, we have about 50,000 square feet of heated floors scattered in 15 car washes and some of those floors have some serious cracking after 30 years. The only places that have developed leaks in the tubing (polybutylene) are next to the edge of the heated slab in a couple of instances where a corner broke off. The older copper underground distribution lines, however, have been more problematic. When those go bad, we re-pipe the distribution overhead and down the walls.

 

[tdkkart]

I would think that as long as you have rebar in the concrete, including across the areas where the control cuts are made, you are not going to get much if any displacement between the slabs. If you don't have displacement you shouldn't have problem with breaking the pex.
This is why I don't like wire in concrete, it's simply too small to prevent the concrete from moving. When concrete decides to move, it moves, and I've seen it break wire.

 

[jklingel]

Egads: Wow. Lots of questions there. Before I ran ANY pipe, I'd do a heat-loss analysis to see how many btu's you are going to need. That will influence both the size and spacing of the PEX and the temp and flow rate of the water going through it. If you go by "feel" and get it wrong, how are you going to fix it? Everywhere I read says to put the hottest pipes of any loop along the outside edge (typically more closely spaced there), then work your way in, then back to the manifold. 1/2" PEX should not be run longer than 300', and 5/8" about 450 (manifold to manifold). That said, a plumber I know just re-tooled a poorly working floor that another guy did and managed to get satisfactory results w/ 800' runs; "satisfactory", not "good". John Siegenthaler's book "Modern Hydronic Heating" (and/or others) is something anyone installing hydronic heating should read, IMO. I am, and am learning lots. Good luck w/ the job. j

 

[egads74]

Thanks for all the feedback...
obsessive... yes... but for the one chance I get to do this right. this could be a costly mistake...
My heat guy did the heat loss calc.. and was the one who said to go no wider than 9". Of course all the tube manufactures said 12" oc. is sufficient in all their dealings of this nature and concrete will get only so hot with content of tube coming back hot...

Also in comparison of tube stapled to foam at bottom of concrete... the better way is 1/3 way up... attached to rebar... the rebar will improve performance through better distribution of heat... attach every 2 feet to avoid tube floating in cement. Also saw use of 2 layer rebar offset with tube in the middle of sandwich.

One pex supplier told me of an installation where trucks go over floor and concrete moves and they see the pex stretch a bit and as concrete moves back into position so does the pex. they had their eye on it for 6 years now.. Point he was making is the pex is flexible to an extent... I do not know all the details of this stress testing...

 

[jklingel]

... but for the one chance I get to do this right. this could be a costly mistake... •• No doubt. Worry time is now, not after the mud hits. I know that I will fuss w/ mine and wonder until the first day it is -40 and it works...

My heat guy did the heat loss calc.. and was the one who said to go no wider than 9". •• If he knows his stuff, then you've got it. The spacing and water temp is all about how much heat you need and how hot you want the floor. Sounds like it is under control.

Also in comparison of tube stapled to foam at bottom of concrete... the better way is 1/3 way up... attached to rebar... the rebar will improve performance through better distribution of heat... attach every 2 feet to avoid tube floating in cement. Also saw use of 2 layer rebar offset with tube in the middle of sandwich. •• I've read the same, and to NOT attach on bends. One just has to hope the mudslingers don't lift the rebar to get it "in the middle" and lift it too far, if they do that.

One pex supplier told me of an installation where trucks go over floor and concrete moves and they see the pex stretch a bit and as concrete moves back into position so does the pex. •• It is hard to think of concrete flexing, but I have read that the corners will curl on a large slab that dries too quickly. Too, one would think (I used to, anyway) that a 900' oil tanker is quite stiff, but my dad has been on them on one end and watched the middle rise a few feet in heavy seas...