New to {PEX} --manifolds vs. Tees

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Old 06-04-13, 11:00 AM
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New to {PEX} --manifolds vs. Tees

Looking ahead to re-plumbing my cottage I think I'm going to choose PEX over copper or pvc. I'm planning to replace everything all the way back to the pump. I'm wondering about the use of manifolds in PEX system design. This is a diagram of my floorplan with proposed piping overlayed. Does this really make more sense than branched lines? Is the idea to end up with more consistant flow at each terminal, or is it just cheaper/quicker to do it this way? Would a 4 or 6-port 3/4" in, 1/2" out manifold do it?

I've laid out the plan so all plumbing is in-line so either approach seems appropriate. The water from the pump would run directly to the boiler & HWH (I assume I would use tees on this section), then from the manifolds it distributes to:
(hot & cold)
kitchen sink
shower
bathroom sink
laundry tub
(cold only)
toilet

A modest system that wouldn't break the bank to use copper but I like the freeze-proof quality of PEX.

 

Last edited by lawrosa; 06-05-13 at 09:20 AM. Reason: Spelling in header
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Old 06-04-13, 11:13 AM
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IMO I would run 1" mains from pump to bath groups. Then brak down from there. Probably right to 1/2".

On a well you want to keep volume.

( I did the same on my home thats also on a well. No loss of flow when using multiple fixures. )
 
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Old 06-04-13, 07:27 PM
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By "bath groups" are you saying I should have separate manifolds for different areas? I was hoping one hot & one cold would be enough for a system this size.
 
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Old 06-04-13, 09:46 PM
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No manifold at all. Just a H/C trunk lines, They tee off from that...

oh cottage? I would just run 3/4. Where the manifolds are in your pick just make the turn with 3/4 too. Tee off as you move along is all.

I never understood the manifold thing......
 
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Old 06-05-13, 07:28 AM
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Originally Posted by lawrosa
I never understood the manifold thing......
Me either and that's why I asked. Seems from web reading that most installs use the manifolds with all lines extending out from it. No tees anywhere. Sounds wasteful but there must be a good reason for it. Maybe it's more foolproof (less crimps, less chance for leaks)? Maybe you just get hot water faster since the entire volume of cooled water in a large supply pipe doesn't have to be evacuated before the hot can reach the end of the line?
I do like that each manifold tap has its own shutoff valve. If the manifold was located in an accessible spot those valves could be handier than shutoffs at the terminal end.
 
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Old 06-05-13, 07:31 AM
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Mike I just noticed your change to the topic title--what it REX?
 
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Old 06-05-13, 07:34 AM
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You put REX. I added pex. I assume thats what you ment but did not want to correct it. Possibly there is a new type of pipe called REX that I dont know about....
 
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Old 06-05-13, 08:01 AM
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Oops--now that's really a stupid goof
Feel free to swap PEX for REX.
 
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Old 06-05-13, 09:47 AM
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The idea of valves to shut off each fixture group is interesting, until you realize that it's something so rarely done, it's not worth it. I would only consider a manifold if there were under-slab runs or something where a leak would need to be isolated and shut off for maybe an extended period of time.

While you're running all these new lines, don't forget about an exterior faucet or two!
 
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Old 06-05-13, 09:52 AM
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Also, just to clarify:
...freeze-proof quality of PEX.
PEX isn't freeze-proof. It can still crack/split if frozen with water inside. It's just less likely to have an issue than copper or PVC/CPVC. If it's not going to be used over a cold winter, it should still be drained.
 
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Old 06-05-13, 11:07 AM
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Where does the topic moderator stand on hub vs. in-line branching?

Anyone else?
 
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Old 06-05-13, 06:41 PM
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The manifolds look nice if you have a mechanical room and want to show it off to your friends. They can be fed from the top and bottom of the manifold to allow for a better balanced flow to all fixtures at the same time and have the added feature of cut off valves if ever needed. A plus is no fittings in the floor or walls as you run the line directly from the manifold to the fixture. The cost of pipe is dirt cheap.
Basic set up is a main line with tees to the fixtures and cut offs at the fixtures.
If by chance you are running the washing machine, dish washer, watering the lawn and filling the bath at the same time, the flow to the last fixture may be a bit less.
 
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Old 06-05-13, 07:18 PM
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Where does the topic moderator stand on hub vs. in-line branching?

My bad. When I think manifold I was thinking homeruns.

I dont and never used homeruns, What I douse is standard branching for large homes. I increase the main lines significantly for these apps. Often and always 1".

Lastly for smaller homes I do use the end manifold type piping. Although I simple just tee off at the end. Manifold? Not really. Just tees. So really its a branched system, but just so happens all the plumbing is grouped together.

PEX Plumbing - Trunk & Branch Plumbing - Residential PEX Manifold Plumbing - Home Run Plumbing Layouts

Something to think about...
 
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Old 06-06-13, 09:42 AM
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I'm still undecided. It might come down to whether the tubing & manifold will fit where I would like to put it. Most of the plumbing on my diagram is in the center section of the house--which is on a crawl. The large rear section is is over a basement. I'd like to put the piping in the basement area for easier access but only if it will tuck in the space between joists so I can put up a nice ceiling (with access to the manifolds). Once penetrated into the crawl all the tubes can be hung under the joists there. It would be easier to punch the supply lines into the crawl and do all the rest of the plumbing there. No joist drilling, no need to hide the work--but then access is more limited after the job is done.
 
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