Distribution pipe size - 26.4 GPM.

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by Rossn, Apr 22, 2021.

  1. Rossn

    Rossn Member

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    Using IPC 2015, I get 26.4 GPM (40.3 WSFUs combined) for my 4.5 bath home. I was previously advised by Jeff that for my baths, you would typically see 1-1/4" or 1-1/2" for the main distribution line in the home.

    Now that I have the above numbers, am I OK with 1-1/4" Copper (L) main distribution line within the home, or do I need to bump up to 1-1-/2" Copper (L)?
    Around 50'.

    I do like drink of cold water, only have 4-5 people here regularly, and some devices such as the Moen Flo only size up to 1-1/4". I think it would be uncommon I would practically use > 18 GPM.
     
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    The dynamic pressure loss (without taking into account fittings and changes of direction) with 27gpm on 1-1/4" pipe is about 2.3psi. It drops to 1.2 psi for 1-1/2", and the velocity drops by about 1fps with the larger pipe, but still within the recommendations of the Copper Institute.
     
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  4. Rossn

    Rossn Member

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    Ok, thanks - sounds like there is not any practical concern, given using that volume would be a rare-likely-never event. Thank you, Jim!
     
  5. Reach4

    Reach4 Well-Known Member

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    I am skeptical. Got a link for that? Are you sure that was not talking about a service line to the home, and you extrapolated/extended that to what you should run to your bathrooms in the home?

    For service to the home, cities often mandate bigger lines. Even if your particular city does not, extra capacity for future needs can be a good idea. Plus bigger service pipe minimizes pressure loss if the water pressure from the city is low. Fire sprinklers and irrigation could be future water uses. Probably not going to put in a pool in the Denver area, however.
     
    Last edited: Apr 23, 2021
  6. Rossn

    Rossn Member

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    Correct, main distribution line in the home, and my WSFU's seem to support that. I'm not sure how to link to a specific comment, but it is in this thread:

    Now that I have new numbers, I had forgotten the details of the comment and his thoughts on moving up, if near the limits. Based on pressure loss that Jim shared being OK, and velocity being closer to 7FPS, it seems I should be fine with 1-1/4, which works well, given I have press jaws of that size already, and that is the largest available Moen Flo. I also think IPC is pretty high on their estimation at 26.4 GPM - that is a lot of water.

    My 1" service line (which has an issue) is way too small. It likely needs to be 1-1/2 for that 275' run from the meter.

    Edit - I'm referring to the main distribution line from entering the home to the mechanical room, not the branches - perhaps I am not using the terminology as I should.
     
  7. Reach4

    Reach4 Well-Known Member

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    I see what happened.
    "I'd be coming in house with 1-1/4" or 1-1/2" . and the service to house in future I'd run 1-1/2" I don't think 2 inch be needed but you're not doing that now. upping meter size is a consideration as well but again not dealing with that now"​
    was referring to the service line from the city, not the piping around the house. The wording could have been "I'd be coming into the house with 1-1/4" or 1-1/2" to express the intent with less chance of misinterpretation.

    Once you come into the house and tee off to the outside hose bibs, hot water, port for future expansion, etc, you don't need such big pipe.

    I suspect you should take 1 inch to the WH, which is what the big-honker water heaters expect. Regular water heaters get 3/4 coming in. After the water heater, avoid oversizing the hot lines, because it takes a lot longer for hot to arrive if you don't have hot water recirculation.

    If you have a water softener, that could be 1 inch in or 1-1/4 inch in, depending on the softener.
     
  8. Jeff H Young

    Jeff H Young In the Trades

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    Dont mean to confuse but I think you'd have 1 1/4 minimum entering building . the hot wont be under 1 inch and the cold wont either befor picking up fixtures . because of all the long run and all the fixtures just a 3/4 line would be small even just on the hot.
    Dont know anything about the moenflo ? automatic shut off on the main? Ive put some costco type on befor. Remember you can reduce for such a device and then increase back again. not highly recomended but just like a water meter can be smaller than main dosent mean you cant do it. The valves I installed were 1 inch and instruction said 1 1/4 main was ok
     
  9. Rossn

    Rossn Member

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    Thank you all. Yes, once in the mechanical room things drop in size.

    Jeff, you have been very helpful along the way, and followed what you were saying. I think the 1-1/4" to the mechanical room works and now just have to figure if I need to size the DHW with mixing valve to 1-1/4" (DHW WSFU's say 18 GPM) or if that (as Reach alludes to) is overkill and stick with 1". PDF of plumbing design attached.

    Edit: Yes, the Flo is an auto shutoff if any major leak is detected, amongst other features... but to me, that is high value.
     

    Attached Files:

  10. Reach4

    Reach4 Well-Known Member

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    DHW=Direct hot water, or what?
     
  11. wwhitney

    wwhitney Well-Known Member

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    domestic
     
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  12. Jeff H Young

    Jeff H Young In the Trades

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    Rossyn, you seem to be on track in my opinion looking pretty good. I think that whole house shut off has a real value as well. nothing works perfect every time but certainly a good step to take. I'm not viewing the ISO drawing very well if you figure 1 inch on the hot then that's what it is, not necessarily all the way to the end of your hot line though.
     
  13. Rossn

    Rossn Member

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    Yep, Domestic Hot Water.

    Thanks, Jeff. Even though the WSFU shows 18 GPM, it seems one has to get into commercial mixing valves, etc going to 1-1/4", and I cannot fathom using that, so for the short 5' run and Mixing valve, I'll go 1" copper. My largest heating distribution is 1" Pex, and some of it is home run'd.

    You guys are great. Thanks!!
     
  14. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    The key thing to keep in mind is how much flow would be in any one trunk before it branches off. Then, each branch only needs to handle what's attached to it. This works for both liquids and air, which is why you may often see an HVAC line get smaller as it progresses away from the source.

    If you're building this, I'd seriously consider adding in some return lines so you can either incorporate hot water recirculation, or add it later if you find you are waiting too long for hot to arrive in some (all?) places. Return lines don't need to be large, as a small pump and flow is all that's required to keep it hot, once you turn it on and it has a chance to purge the cold from the line. Keep in mind that if you need to run five gallons out at the end of a long line to get hot, you've dumped five gallons of cold water into your WH, diminishing the hot water volume available. With the lines hot and the tank full, those gallons can go to actually showering, or filling the tub, or whatever comfortably. Code wants those lines insulated, and that is much more easily done during construction than to try to do it later.
     
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