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Discussion Starter · #1 ·
I’m making some progress re-piping our house with PEX in parallel with the galvanized to eventually cut over.

I now have 1” coming from the meter, which tees off to 3/4” over to the hot water heater, but remains 1” as it continues through the rest of the basement. I also have 3/4” coming back from the hot water heater, so the main lines are 1” cold and 3/4” hot, based on a calculation I did for the fixtures in the house, which are quite a few.

I could have a manifold on the wall in the basement which feeds each fixture individually with 1/2” home runs, but that seems like a lot of pipe and could be hard to route upstairs and to some of the other rooms, kind of a mess.

So that leaves either a manifold with some 3/4” runs (to remote manifolds in rooms with more than one fixture) and some 1/2” runs (to any stand-alone fixtures), or go for a more traditional trunk and branch.

The many central shutoffs of a manifold are appealing, but I didn’t know if that was overkill for my situation. With trunk and branch, I would be adding shutoffs on every branch right after the trunk anyway, so maybe that kind of system would eliminate unnecessary extra pipe over to a basement-wall manifold just to come back where it came from to go to the proper room?

Just interested in opinions from those with experience with this, or if anything looks completely wrong - here are a couple potential diagrams:

Main trunks (already in place, not connected to manifold, could tee off to trunks instead)
Handwriting Rectangle Font Slope Wall


Manifold with remote manifolds
Handwriting Rectangle Font Parallel Paper


Trunk and branch (could have remote manifolds)
Handwriting Font Parallel Pattern Slope


Home runs (don’t really want to do this, seems like a mess…)
Handwriting Font Parallel Monochrome Rectangle
 

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IMO (and I'm not a full time licensed plumber), a lot of this has to do with personal preference and prioritizing. You'll hear a few things here that you already know, so some of it simply has to do with you sorting your own priorities out. Early manifold - organized, puts things in one place, kind of nice for the OCD crowd. But higher material cost and only you know how hard it would be to do all that routing to some of the upper rooms. So I wouldn't call it overkill, just personal preference. (You will get a slight reduction in material cost in the homerun compared to what you might think, because everything coming out of the manifold will be 1/2", which is less expensive than the 3/4" (or 1") you'd be running for a trunk.)
 

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Why so many valves for the trunk system? Use stops at the fixture instead. Also, unless your pressure is low, I feel you are oversized in some areas.
 
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Generally, PEX is done with all homeruns, for a few reasons:
1) The piping is relatively cheap compared to the cost of the fittings, so the running single lines is generally fairly comparable cost-wise to add the tees, manifolds, etc. for the branched system
2) With all homeruns connected to a single manifold, you should have no issues with pressure drops.
3) It also allows you to use smaller lines, so you don't have to wait as long for hot water at any one fixture. The volume of water in a 3/4" line is about twice that in a 1/2" line, so you would have to run the water about twice as long to get hot (or cold) water at the fixture.
 

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Discussion Starter · #6 ·
Thanks everyone for the input!

Why so many valves for the trunk system? Use stops at the fixture instead. Also, unless your pressure is low, I feel you are oversized in some areas.
I like the idea of having a valve to close in the basement to isolate the room or fixture so if the stop at the fixture is faulty, other things can go on working. Maybe that’s foolish, since if it was pex, it could just be cut off and a new one crimped back on in seconds. It might be that I’m thinking of things in terms of copper or galvanized that has a lot less slack to work with and requires techniques I’m less comfortable with.

And oversized? That’s a little surprising, considering everything I’ve seen about PEX has suggested sizing up one nominal size over copper/galvanized due to the smaller i.d. - what are the drawbacks of an oversized 1” trunk on an average city supply?
 

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Yeah PEX is great in the sense that you can work on it wet, and push-to-connect fittings can always be used in a pinch. In theory sizing up is the right thing to do so as not to decrease internal diameter, in practice I've never seen a problem as the water flow is still within the threshold of what seems like good water flow. In other words, if I changed all the 1/2" copper in your house to 1/2" PEX overnight without you knowing, you likely wouldn't notice any difference.
 

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what are the drawbacks of an oversized 1” trunk on an average city supply?
Probably not any drawbacks for the trunk line, but as I alluded to, oversizing the the lines to the fixtures, especially the hot water, can result in longer waits for hot water and more water down the drain before it's hot enough to be usable for some things.
 

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I agree with your sizing, I did the same thing when doing my home. Given size of pex vs copper, pex flows less gallons.
 

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Discussion Starter · #10 ·
I think my concern is running four 1/2” homeruns from the basement to the 1st floor laundry room (which is in an addition with no crawlspace), ten up to the 1st floor bathroom, and five of those up to the second floor bathroom…

would be potentially a lot more difficult as a retrofit situation in this old house than just running two 3/4” to the laundry, four 3/4” up to the bathroom, and two of those 3/4” up to the second floor bathroom (or even just two 3/4” to the first floor bath and teeing those to continue upstairs, as it likely is now).

There’s also the matter of me not even knowing exactly where the supply runs in the bathroom over to the tub in the second floor bathroom - I’m guessing under the floor, but that would have to be perpendicular to the joists, not sure if they ran it along the exterior wall… so if I just had to run a couple supplies from a bathroom manifold, might be easier than a long homerun all the way from the basement?
 

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I am going through the same debates right now, trying to design something to replace the old PB piping.

I will be running PEX as well with manifolds in the garage one for cold one for hot.

Should you run a different home run line for each fixture? I think it depends on the situation.

Like you, I have debated if I have 4 outside spigots do I put in 4 home runs? Because in my case I have one that's 7 feet away from the manifold, one that is 18' away in the other direction, and then the other two that one of them teed off the other because they are both 40'+ away. Compounding this further, I have a fifth spigot, that branched off a kitchen line inside the exterior block wall. It is impossible to have a home run for that spigot unless I tear into the wall to isolate it. Then I have another bathroom where the cold supply enters the bathroom and there are branches inside the wall that go to the toilet and shower same with hot. So once I decided that tearing up the interior and exterior walls to isolate these branches into individual runs, my option of having a dedicated home run for each fixture is no longer.

I also debated what the benefit of every fixture having a home run is. To me the benefit is you can shutoff a shower to say change a cartridge with the toilet still flushable, or shutoff the icemaker line without having to shutoff the cold side of the kitchen faucet. But how big is that benefit? If it's a one bathroom house it's important, if it's a 4 bathroom house I don't see it being critical. I also wonder do I really want four lines stubbing out of the kitchen sink cabinet wall, two for cold (ice maker, faucet), two for hot (faucet, dishwasher), or do I want to use dual handle shutoff valves? In addition, having individual home runs on the hot side increases wait time. Think about a bathroom, you turn on the lav sink to wait 40 seconds for the hot water to come to wash up or shave. Then you hop into the shower, if the shower hot side is on a home run, you wait 40 seconds AGAIN for the water to get hot. A trunk and branch you get hot water immediately.

Another factor is access. If you have a full basement where the piping is easily accessible, it's an easier decision. In my case, I have a creepy low headroom crawlspace. Minimizing joints is a consideration where trunk and branch means more joints.

I end up planning a hybrid. I will do a home run for most fixtures on the cold side, but more trunk and branch on the hot side. Two lines for 5 outside spigots.
 

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I also wonder do I really want four lines stubbing out of the kitchen sink cabinet wall, two for cold (ice maker, faucet), two for hot (faucet, dishwasher), or do I want to use dual handle shutoff valves?
"Branching" inside the cabinet is typical, even in what's considered a 'homerun' system.
In addition, having individual home runs on the hot side increases wait time. Think about a bathroom, you turn on the lav sink to wait 40 seconds for the hot water to come to wash up or shave. Then you hop into the shower, if the shower hot side is on a home run, you wait 40 seconds AGAIN for the water to get hot. A trunk and branch you get hot water immediately.
It depends on what you do. The wait time to get hot water at the first fixture you turn on will be longer with a trunk and branch system, because the volume of water in the line is greater. The same length of 3/4" line has more than twice the volume of a 1/2" line, and total length of the lines will likely be lat least a little longer than having a line run directly to each fixture. So yeah, wait 90 seconds for hot water at the lav, and you'll have hot water sooner at the shower if you jump in the shower after running the lav faucet. If not, you're waiting longer for hot water at the lav and waiting longer for hot water in the shower, if you don't use both at the same time. I don't find myself using the lav and then jumping in the shower all that often. Usually, it's one or the other.

The more common reason to employ a homerun system is to avoid pressure drops at one fixture when another is turned on at the same time (the classic 'scald the guy in shower by flushing the toilet' issue, for instance). There's also fewer connections and no intermediate connections, often in hidden and/or inaccessible locations, which is where leaks most often occur. The tees, etc. are also expensive, relative to the cost of the pipe, so the total cost usually ends up about the same.

That said, branching for outside spigots makes sense, since temperature and pressure variations are of little consequence there.
 

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Discussion Starter · #13 ·
Okay, I think I’m going to build my own manifold in the basement but not home run to every single fixture. I’ll follow the “cold manifold with remote” diagram from my first post, with a corresponding hot, and use the same general design from the finehomebuilding “build your own pex manifold” article.

Now the question is: do I spend a little more for brass tees and fittings to construct the manifolds, or use the poly/plastic fittings and/or ball valves?
 

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"Branching" inside the cabinet is typical, even in what's considered a 'homerun' system.

It depends on what you do. The wait time to get hot water at the first fixture you turn on will be longer with a trunk and branch system, because the volume of water in the line is greater. The same length of 3/4" line has more than twice the volume of a 1/2" line, and total length of the lines will likely be lat least a little longer than having a line run directly to each fixture. So yeah, wait 90 seconds for hot water at the lav, and you'll have hot water sooner at the shower if you jump in the shower after running the lav faucet. If not, you're waiting longer for hot water at the lav and waiting longer for hot water in the shower, if you don't use both at the same time. I don't find myself using the lav and then jumping in the shower all that often. Usually, it's one or the other.

The more common reason to employ a homerun system is to avoid pressure drops at one fixture when another is turned on at the same time (the classic 'scald the guy in shower by flushing the toilet' issue, for instance). There's also fewer connections and no intermediate connections, often in hidden and/or inaccessible locations, which is where leaks most often occur. The tees, etc. are also expensive, relative to the cost of the pipe, so the total cost usually ends up about the same.

That said, branching for outside spigots makes sense, since temperature and pressure variations are of little consequence there.
To me, the main benefit of the home run system is the elimination of additional joints and isolation of some fixtures for repair without having to shut down more fixture than necessary.

If one goes total OCD on really every fixture, meaning a home run to the icemaker, a home run to each spigot, a home run to the dishwasher, then unless it's new construction, it means opening up walls to separate existing tees inside walls. I bet every master bathroom with a "his sink" and "her sink" have tees in the hot and cold side in the wall and can't be easily isolated. So my point is if the decision is to not open up walls to expose every supply tee, it will be "mostly home runs" and not 100% home runs anyway.

When it comes down to it, say in a bathroom, the true benefit of having a home run to every fixture, in my view, is just the shower. You already have a shutoff at a toilet, a shutoff at the lav sink, so those two can be turned off or no if needed. The real practical issue is the shower where typically there is no easy shutoffs. Either there is none, or the shutoff is on each side of the valve only accessible by removing the wider trim plate which is typically caulked in. So in the event you have a broken cartridge, or a leaking seat in the handles, you take it apart and go look for parts or order one online, it takes time and meanwhile you can't use the shower, but you can't use the lav and toilet as well, the whole bathroom is shutdown till then. Having a home run to the shower allow the other two fixtures to keep running.

The pressure loss from flushing a toilet while taking a shower don't really happen in modern days. With so many tub and shower valves being pressure balanced and reduction of the cold side inlet will be automatically compensated by the hot side.

I had one neighbor repiped and did home runs for EVERYTHING. It was interesting to look at what he did. I find two things peculiar. First, when the line runs from the water meter to his house, the a riser comes up to the house shutoff, then continue up and entered the house...he has a hose bibb right there. He used to tee off that line after the shutoff before it enters the house (as most houses do), he ran a line from the garage 50' back to this hose bibb, he said he did that because it allows him to control that bibb from the garage. I find that interesting. It definitely let him service that bibb without turning the entire house off, but that's 50' more pipe. Those are hard decisions. However, as I looked at his multiple home runs, I see intermediate couplings along the run, he said that is because he wanted to use all his tubing. So he may have a 100' reel, and on one run he has 18' left on one reel, and he can throw that away or connect a 12' piece to complete the run, so he put in extra couplings, which to me kind of defeats the purpose somewhat.
 

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Okay, I think I’m going to build my own manifold in the basement but not home run to every single fixture. I’ll follow the “cold manifold with remote” diagram from my first post, with a corresponding hot, and use the same general design from the finehomebuilding “build your own pex manifold” article.

Now the question is: do I spend a little more for brass tees and fittings to construct the manifolds, or use the poly/plastic fittings and/or ball valves?
It is standard practice for plumbing contractors in my area to use plastic fittings, brass valves. I have not heard of any plastic failures, ever. I cannot say the same for brass.

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Discussion Starter · #16 ·
The pressure loss from flushing a toilet while taking a shower don't really happen in modern days. With so many tub and shower valves being pressure balanced and reduction of the cold side inlet will be automatically compensated by the hot side.
Oh, so the person showering will just get scalded?:cool: But seriously, thank you for that example as it gives me something to think about with my

It is standard practice for plumbing contractors in my area to use plastic fittings, brass valves. I have not heard of any plastic failures, ever. I cannot say the same for brass.
Thank you. I think I’ll spring for the lead-free brass ball valves, and go with plastic for all the elbows and tees, at least at the manifold.
 

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Oh, so the person showering will just get scalded?
The pressure balance mechanism in the modern shower valves is meant to alleviate the scalding issue. It compensates by reducing the hot water to keep the same ratio of hot to cold when the cold pressure drops.

Scalding isn't the issue if you have that type of shower valve, but there can still be a noticeable loss of pressure in some cases, especially if the washer branches off the same trunk line. The toilet usually doesn't cause an issue.
 

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Whatever you do, when you get to the piping of a shower or tub valve, if the valve does not have an integral diverter but uses a pull-up diverter on the tub spout, do not use PEX there to the shower head. It has been demonstrated many many times the restriction of the crimp or clamp style PEX fittings there will result in water coming out of both the spout and the shower. Follow manufacturers instructions as by now most brands of shower valves should have the "do not use PEX" warning to go from valve or twin el to shower outlet by now.
 
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