Fixture Unit Values - Pipe Sizing for remodel

Discussion in 'IPC Plumbing Code Questions' started by supernal_pipe, Aug 11, 2017.

  1. supernal_pipe

    supernal_pipe New Member

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    Aug 11, 2017
    Location:
    Denver
    2009 IPC Table E201.1 - Fixture Unit Values


    I'm currently doing a remodel, and the owner is asking me to size up the lines to accommodate an additional bathroom, and kitchen.

    House currently has a 3/4 inch service pipe, and that same 3/4 inch size is currently extended as the Distribution pipe to all other fixtures in the house.
    ( branch system )

    According to Code, a 3/4 inch service pipe, expanded up to a 1 1/4" distribution pipe at 60 feet of developed length will give me an additional 24.5 WSFU. (32 - 7.5)

    Which is what i need to handle his proposed load.

    My question is, why does this work?

    Code says it will work, but how does adding a length of bigger pipe ( 1 1/4 inches ) after the city supplied 3/4 inch pipe allow for 24.5 more wsfu ??

    Is it simply that the larger pipe segment increases pressure for everything after the larger pipe size?

    The table lists maximum development length, however, to have the needed effect, is there a minimum pipe length for increasing the diameter to provide the additional wsfu's?

    I assume i can add a segment of 1 1/4 inch pipe after the hot water heater to provide more "fixture unit value's" for the fixtures downstream?
    If yes, how long should that segment be?
     
  2. Reach4

    Reach4 Well-Known Member

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    Sep 25, 2013
    Location:
    IL
    What are you describing? Are you talking about 3/4 from the meter, for a few feet, and then 60 feet of 3/4 inch, or are you talking about 60 ft of 3/4 and some additional length of 1.25 inch pipe after that?

    A length of pipe will have a pressure drop with a particular flow rate going thru it. That is followed by another length of pipe with a pressure drop with that same flow rate going thru it. The pressure drop will be the sum of the two pressure drops.

    Do you understand resistors and voltage and current? We could make an analogy to that.

    What is not a good analogy is a mile single lane of road carrying xx cars per hour followed by a 100 mile distance of 4 lanes traveling your way. In the road analogy, the single lane section will limit how many cars per hour the combined sections would carry. With water pipe it is not the same. https://www.hy-techroofdrains.com/water-flow-through-a-pipe/ shows that you could get a lot of water through 5 ft of 3/4 pipe. There would be some drop, but it would not be that much for 5 ft. If you then expand to 1.25, you will not get a lot of additional drop for the next 100 ft. But having another 100 ft 3/4 inch pipe would give a lot more drop.

    I am confident you could find a better pipe calculator for this purpose.
     
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  4. supernal_pipe

    supernal_pipe New Member

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    Start
    City supply @ 3/4" pipe, 20 feet to house ( Service Pipe ) increased diameter to feed Distribution pipe
    Inside house @ 1 1/4" pipe, 20 feet to water heater ( Distribution Pipe )
    At water heater, 1 1/4" reduced to 3/4", 4 feet of pipe to feed water heater. + branch reduced to 3/4 inch to feed bathrooms, kitchen etc.


    Code says this will work, i'm trying to understand WHY it will work.
    * esp before actually trying it...
     

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  5. supernal_pipe

    supernal_pipe New Member

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  6. Terry

    Terry Administrator Staff Member

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    Plumber
    Location:
    Bothell, Washington
    It's all about friction loss.
    An awful lot of water will pass through a 3/4 meter, but then if you run a long 3/4" line to the home, there is very little at the end of that. Think of a very small straw and a milk shake. There is plenty of milk shake there, but the bigger straw gets the job done much better.
    On my parents home, they had 250 feet of 3/4". That was to small to add irrigation to the back of the lot. Changing the line to 1-1/2" for most of the distance allowed seven sprinkler heads to run. They have a 5/8" meter. It made a huge difference changing to the larger 1-1/2" pipe size.

    [​IMG]
     
    Last edited: Jan 24, 2021
  7. supernal_pipe

    supernal_pipe New Member

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    I think i believe you...
    2.54 psi of loss (3/4 inch pipe) compared to .31 psi ( 1 1/4 inch pipe) is a large difference.
     

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  8. hj

    hj Master Plumber

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    Aug 31, 2004
    Occupation:
    Plumber
    Location:
    Cave Creek, Arizona
    quote' , i'm trying to understand WHY it will work.

    It WON'T work, unless your 3/4" pipe has the capacity to deliver that much water at that pressure and flow, which will depend on how LONG the smaller pipe is. a 100' of 1/2" pipe will ONLY deliver a certain maximum flow, regardless of how large the rest of the pipe is.
     
  9. supernal_pipe

    supernal_pipe New Member

    Joined:
    Aug 11, 2017
    Location:
    Denver
    Flow gets restored when the diameter is reduced back to 3/4 of an inch before it hits fixtures.
    During it's time in the thicker pipe, water experience far less resistance to flow, their by allowing a 3/4 inch pipe to supply it's full amount of fixtures at a distance.

    So, start 3/4, transmit though ( at slower flow rate, with no resistance ) 1 1/4 inch pipe to get to the back of the property, then step back down to a 3/4 inch branch to supply fixtures that all tap into the 3/4 with 1/2 inch pipe

    3/4 ( source ) into 1 inch over 100 feet can support 16.5 WSFU's
    where as
    3/4 ( source ) into 3/4 over 100 feet can support 5.5 WSFU's


    Water in in-compressible so this should be fine.





    Code says it works, via table E201.1 (icc.ipc 2009)
    Physics says it works, via the two provided links.
    *( physics links aren't taking into account resistance, cause physic's equations rarely do... )
    Table E103.3 does show resistances in lines based upon the connectors used.... and Does back this idea up.

    Terry says it works, from experience.

    Why do you say it won't work?
    Are Water Supply Fixture Unit Values not accurate?
     

    Attached Files:

    Last edited: Aug 15, 2017
  10. supernal_pipe

    supernal_pipe New Member

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    Location:
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    Maybe i misunderstand what table E201.1 is trying to tell me?
     
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