Best practice for Poly-b repipe

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David Yates

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I am thinking of assisting a friend that will probably do a re-pipe of a modest 1980s house that has poly b pipe.

Plan to replace with pex....

Is there a way of planning the re-pipe that is labor efficient? I see a LOT of drywall repair in the future but am curious about the challenge around shower control valves etc...

Any good website referrals (or sage advice )

Dave
 

Jadnashua

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You may want to consider manifolds verses trunk and branch (if that's what's there). Also, the ID of pex is fairly small, so your main line may need to be larger than what you think. A 1/2" line should only really feed one thing. A 3/4" will flow about 2x the volume of a 1/2" line. You may want to run a dedicated hot water return line in case you want to add hot water circulation system later rather than using a cross-over valve and the cold water line as the return. Pex is floppy which means it is harder to make it look neat (but hidden in a wall, it really isn't a big deal!). For optimum operation, take advantage of the bendability of the stuff and avoid extra fittings to turn corners unless absolutely necessary. If you need a sharp corner, use a bend support. It looks more professional to use a copper stubout coming out of the wall for shutoffs for say sinks, toilets, etc. verses having the floppy pex there. They make copper stubouts designed to be anchored to the studs so your valve has something solid to hold it. Pex-A tubing is more flexible than the -B or -C variants, which means it can turn a smaller diameter corner without kinking. You don't want to make the holes too small, as when you try to thread the tubing through, you could end up scoring or binding and are more likely to crimp it. Type -A is the only one that can repair a kink without cutting it out and replacing it with a fitting. When using -A stuff, you can use expansion fittings which have less restrictions than those that use a crimp. If you decide to go with crimp fittings, make sure your tool is calibrated, or your test tool is the right one to verify you've crimped them properly.

Around the shower, if this is a tub/shower, you CANNOT use pex to the tub spout...it must be full-sized piping, and best with copper, or you'll have problems with the shower heads dribbling while filling the tub.
 

David Yates

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Thanks for the info. I may do a hybrid system like the Uponor system (half way between a home run and trunk and branch system)

Does it make sense to start at the upper level of the house and work down? Assuming we can get to the back of the shower/tub valve what cahallenges are there with switching to pex?

Aside from being “tidy” is there anything wrong with leaving the old poly b pipes in the walls?

Dave
 

Jadnashua

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On the tub/shower...you cannot use pex from the valve to the spout (must be full diameter ID of copper or brass), but other than that, if you size things properly, shouldn't be an issue. Running any water supply pipes in the attic can be problematic. If it's a must, the pipes must be under the insulation, near the ceiling below so some room heat will keep them from freezing, and help to keep them from getting super hot during the summer. Also, pex cannot be exposed to UV long-term (most limit it to about 30-days during construction), or it will start to degrade.
 

David Yates

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I have heard that cautionary note regarding the tub spout before. I have only installed one tub spout before. I ran the supply line from the mixing valve (Riobel) down to a drop ell. The drop ell was then attached to a copper threaded nipple which attached to the tub faucet.

Did I mess up?
 

FullySprinklered

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I've done a couple of repipes where it was cost effective to just put new faucets in. Otherwise, you would have to spend some expensive time installing fittings to accommodate the new pipe at all the connections on the t/s valve.

The tub spout absolutely has to be rigid. Pex ain't.
 

David Yates

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I have to believe that a brass nipple firmly screwed into a drop ell (which is screwed into a framing 2x4 is as rigid as a copper pipe?

Perhaps we are at cross purposes.
 

Reach4

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Yes. Perhaps we are at cross purposes.
Yes. I think there is more going on than meets the eye.
bpf8004-01.jpg
 

Jadnashua

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The requirement, all manufacturers have that I've seen, is that you need full diameter tubing to feed the tub spout. Using pex to a drop-ear twin-el probably would work if you used a brass nipple to the spout. There must be less restriction to the spout than the showerhead feed, or water will back up and likely come out both points. Because you restricted the flow to BOTH of them, and then made the outlet larger for the spout, it would work, but using pex will decrease the flow rate and you won't fill your tub as fast as you could if you fed that twin-el with solid tubing.

If your valve has two ports, one for the showerhead and one for the tub spout, using pex for the tub spout will NOT work. When using a twin-el, you're only using one port on the valve, so the spout would still have less restriction than the showerhead.
 

Reach4

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That drop ear fitting I pictured is 3/4 inch PEX to 1/2 NPT.
 

Jadnashua

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He said he had a twin-ell in there...I haven't seen a twin-ell designed for pex, nor have I really looked for one. The twin-ells I have seen do not have ears on them to anchor things to blocking. Doesn't' mean they don't exist.

If you feed the twin-ell somehow with pex, and the larger outlet with a nipple to the spout, because the spout would then have a larger, less restrictive opening, you shouldn't get any backup into the showerhead, regardless of what type of tubing you used for it.
 
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He said he had a twin-ell in there...I haven't seen a twin-ell designed for pex, nor have I really looked for one. The twin-ells I have seen do not have ears on them to anchor things to blocking. Doesn't' mean they don't exist.

If you feed the twin-ell somehow with pex, and the larger outlet with a nipple to the spout, because the spout would then have a larger, less restrictive opening, you shouldn't get any backup into the showerhead, regardless of what type of tubing you used for it.
You can't have a flow restriction anywhere on the spout line or the shower head will dribble. There are plenty of drop ear pex elbows commonly available, but you would have to make sure the pex and it's adapters were non restrictive enough to match copper or brass 1/2" npt. It's going to cost you more in materials to make pex work than it is worth.
 

Jadnashua

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It's the restriction in the twin-ell and after it that is critical. ANy restriction prior to that twin-ell will just end up with restrictions to BOTH the spout and the showerhead, but with the mandatory restriction in the showerhead, if the spout's inlet is full diameter, it won't matter. If we're just talking about a simple ell, then yes, pex will cause a problem, but not when the only output of the shower/tub valve is feeding a twin-ell and the spout is kept full diameter from it.
 
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