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1950s house with original galvanized pipes. Looking to repipe with PEX. Currently low water pressure, takes minute(s) for hot water to reach back of house, very hard water with occasional orange/brown tinge water from the sink spout. Small home, 1200sf with two bathrooms, washer, laundry sink, kitchen sink. There's a crawlspace, and one bathroom is currently gutted to the studs, allowing access to all plumbing for both bathrooms. Line coming in from city is 1" galvanized. Rusted and nearly busted! ~30' between my house and the city water line running into a box in my back yard. Got a quote for the job... $12k! So here I am on a DIY forum.

Plan: Trunk and branch setup. Replace city line with 1" copper, buried 18". Reduce to 3/4" PEX immediately once in crawlspace (same plan the repipe salesman had) Keep 3/4" for all cold lines, branching to 1/2" for fixtures. PEX B (home Depot) with stainless crimps.

Questions!

  1. Should I do the same for hot water lines -- 3/4", branching to 1/2" for fixtures? Or use 1/2" throughout from the water heater and branching to fixtures? Reason I ask is the company that quoted me $12K said they'd opt for 1/2" for hot water. I assume this means hot water would arrive to the fixture more quickly. Is this much better than 3"4" split to 1/2" anyway? Is there a significant benefit to a smaller line for hot? Thoughts?
  2. plastic vs. brass fittings?
  3. cinching vs. expansion fittings?
  4. Need I replace the city line ASAP, or can I save this for later? Other than asking for trouble down the line, would it pose an immediate to run a new PEX system with an old city line?

I've "done my research" but am seeking guidance specific to my setup. Thanks!

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    questions seeking an opinion are off topic here ... this site is not a forum ... it is a Q&A site ... please ask ONE specific, answerable question
    – jsotola
    Commented Oct 20, 2021 at 23:31
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    I would suggest going from 1" to TWO 3/4": lines, one to feed the water heater, one to feed the colds, rather than one 3/4 to feed the whole house.
    – Ecnerwal
    Commented Oct 20, 2021 at 23:49
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    What's the distance from the water heater to where you care about hot water fast? Tubing is cheap enough that you can run longer sections of 1/2" back to a shorter chunk of 3/4", without getting into the whole "manifold as such" arrangement. That will maintain pressure if two are in use better.
    – Ecnerwal
    Commented Oct 20, 2021 at 23:57
  • How long is your service line from the city? (i.e. distance from the water main in the street to where your water service enters your house) Also, who do you have for a water utility?
    – ThreePhaseEel
    Commented Oct 21, 2021 at 0:48
  • Jsotola I will edit the text accordingly. I said opinion because I didn't need a full breakdown of pros/cons, but guidance if anyone had a strong preference for one over the other.
    – Travis
    Commented Oct 21, 2021 at 12:06

2 Answers 2

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I can answer the first 3 questions, having done a significant amount of research and a few plumbing repairs on the 3 houses I've owned, first with copper lines, second with pex "homerun" and third with PVC piping.

  1. Yes, line size has a significant effect on availability of hot water, and it comes down to volume. A 3/4" pipe has 2.25x the volume of a 1/2" pipe, and the trunk needs to drain of cooled water before hot water from the water heater will flow to the fixture (remember that hot water in a pipe will cool down close to room temperature over time if it's not flowing). Draining 2.25x the water will take roughly 2.25x as long. Homerun/manifold systems decrease the time a lot by shortening the trunk and branches that need to drain. 1/2" provides enough volume for most fixtures and purposes, but also consider a manifold as it's the perfect time to install one if you're replacing all the plumbing now.

  2. I haven't met a plumber that has strong feelings about brass vs plastic fittings and I've seen both used even in the same house. Homerun systems typically have no elbows to keep every run as straight as possible, but if you're installing trunk/branch you'll need tees and elbows. Cost is probably the biggest factor, but keep in mind if you have hard water or unusual chemistry that can deteriorate brass.

  3. Crimp fittings all day. There are some soft copper rings that crimp down under pressure but in my opinion they're not as reliable for a DIYer as they're difficult to get the same fit every time. Crimp fittings shown below require a tool but the tool ratchets shut and when it releases, it's at the proper compression every time. enter image description here

Another resource I found interesting and useful was a torture test of pex fittings. Obviously this is way beyond pressures you'd see in normal use but if a fitting can stand up to this it should fare well in normal use as well. Can we blow off these PEX fittings? (Youtube link)

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  • Thank you so much for this thorough response. I will look into homerun systems. I want to avoid manifold, I don't think it's necessary in my simple house. I essentially want to replace in-kind with trunk and branch setup, but I'm not set on that. I'll go with stainless steel crimps and plastic fittings. We do have some hard water and as you said, there don't seem to be strong opinions against plastic and they do the job well so the added cost isn't warranted.
    – Travis
    Commented Oct 21, 2021 at 16:20
  • Also, the salesmen tried to tout expansion fittings with plastic fittings, saying crimps break fittings. One of the several points I presumed was to discourage DIY or competitors, as I understood that the $50 crimp tool functioned as a ratchet and was presumably built to minimize the chance to over-tighten. On reddit, someone said crimps further reduce the ID of PEX... I don't see how this is possible, since the fittings are very rigid and shouldn't flex under a crimp.
    – Travis
    Commented Oct 21, 2021 at 17:36
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    By expansion fittings do you mean the fittings for which the PEX tubing is expanded and then slipped over the fitting? If so, this is PEX A or Uponor PEX. The fittings used with Uponor PEX do have a much larger inside diameter than the crimp fittings. The crimp connected fittings have a smaller inside diameter than the PEX tubing and so do restrict flow. View YouTube videos comparing PEX A to PEX B. youtu.be/IZlwvf3vIXs
    – Jim Stewart
    Commented Oct 21, 2021 at 21:25
  • I would like to use PEX A mainly for the flexibility, but still use crimps. I want to run 1" trunk and 1/2" branches to fixtures. Problem is, my local stores carry PEX A only in 1/2" and 3/4". Would it be okay to mix 1" PEX B with 1/2" PEX A? I am still considering expansion fittings, but this would mean settling for 3/4" PEX A which is not ideal and I figure it is better to upsize the trunk to 1" and use crimps.
    – Travis
    Commented Oct 22, 2021 at 13:21
  • You would have to find out if crimp fasteners would work on PEX A. Do not assume they would work correctly.
    – Jim Stewart
    Commented Oct 22, 2021 at 20:21
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I will answer #4 as Frederic did a great job on the first three.

Yes you need to replace the city home run right now for 4 reasons.

  1. Based on things being opened up it will be cheaper.
  2. You need to see how big you can go. If you can go 1" go 1". 3/4" should be the minimum. (For a house that size you do not need more than 1")
  3. You do not want to have to reconnect everything on your homerun. Normal setup is 1" from city, 1" homerun (could go 3/4"), with a couple of of 3/4" lines going to spigots off the city line.
  4. Based on your past issues you could have quite a bit of issues and sediment in this section. Unless it was cleaned out (blown) and there was no build up or rust... why do all that work in your home and not take care of this. This really isn't "plumbing" it is more "digging".
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  • All good reasons. The only reason I had to not do it now is the added work. This all started with a bathroom renovation when I decided I should probably replace the plumbing while it's all exposed. Digging a 30-foot long 18" deep trench, particularly as we are heading into the rainy season, is a whole other job in itself. But DIY jobs have a way of growing, don't they?
    – Travis
    Commented Oct 21, 2021 at 16:25
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    Should be easier to dig and refill during rainy season... think about that too. Also 18" is chump stuff. In Midwest we are 10' at city 3-4' at house.
    – DMoore
    Commented Oct 21, 2021 at 17:01
  • Fair enough. It is actually closer to 36" in some areas but not too bad. I am also not experience with copper and soldering, so was hoping to address that later. Just finding myself strapped for time and energy with a newborn and a house that won't quit! :)
    – Travis
    Commented Oct 21, 2021 at 17:09

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