Why one inch PEX?

Discussion in 'Plumbing Forum, Professional & DIY Advice, Tips & ' started by neosec, Jan 18, 2011.

  1. neosec

    neosec New Member

    Messages:
    2
    Location:
    PA
    I'm helping a friend do some remodeling and found that the water heater has 1" PEX coming from the 3/4" copper ports. It runs about 30 feet into the crawl space before connecting to some existing 3/4" copper that runs ~15 feet where it drops to 1/2" to the master bath. I'm concerned with how long it will take the hot water to reach the master bath due to the volume of the 1" PEX and 3/4" copper. Any idea why 1" pex was used? And is there (much) downside to T'ing into the PEX near the water heater with a 1/2" line for the master bath to get the water there faster?

    Thanks in advance.
  2. Gary Swart

    Gary Swart In the Trades

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    7,302
    Location:
    Yakima WA
    The inside diameter of 3/4" Pex is smaller than the inside diameter of 3/4" copper. I am a great proponent of recirculating systems that will provide instant hot water. The 1/2" pipe will not supply enough flow for a master bath. Compare the areas of 1/2" and 3/4" pipe and you will see it is a huge difference. If you have forgotten, Area = 3.14 x radius squared. Radius is 1/2 of the diameter. I don't know much about Pex other than the size difference.
    Last edited: Jan 19, 2011
  3. hj

    hj Moderator & Master Plumber Staff Member

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    1/2" PEX has about the same volume as 3/8" copper which could be a little small for a bathroom.
  4. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    Location:
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    It also depends on whether you are using crimp or expansion fittings...a crimped fitting further reduces the ID, but because it is short, doesn't affect the flow (much). The expansion system (used by Uphonor) does a better job of maintaining the ID through the fitting.
  5. neosec

    neosec New Member

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    2
    Location:
    PA
    Thanks

    Thanks for the replies. I was not aware of the ID difference. Makes perfect sense now.
  6. jimbo

    jimbo Plumber

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    8,997
    Location:
    San Diego
    There is study going on at IAPMO about the requirement for size of hot water supply hot water to bathrooms. Right now, the code just governs by fixture units. But as we all are aware, lavs and showers today are volume limited to much lower needed amount of water than a kithen or tub. And a lot of WATER is wasted when the volume of the hot supply pipe is larger than really necessary. In the future, look for possible code changes which would mandate smaller size hot water supply to shower and/or lav
  7. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    Location:
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    Someone said that where they live, recirculation systems are required...this also ends up saving both water and energy if it is run on a timer so that it only is running when hot water is normally used AND you've insulated the pipes. Running it 24/7, and the energy savings goes away, but water savings always exists.
  8. hj

    hj Moderator & Master Plumber Staff Member

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    Running the pump 24/7 can prevent pipe failure from constant expansion/contraction as the hot water flows and then cools.
  9. DavidTu

    DavidTu Member

    Messages:
    237
    Location:
    Seattle, WA
    Any opinions/experience with Uponor's record system that uses motion sensors to run the recirc?
  10. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,809
    Location:
    New England
    On any system that only runs when you request it to (like either with a switch or motion sensors), you may need to wait a few minutes to have hot water there when you turn it on. this may be fine if you intend to use it after say taking a dump, but may not be if just going in to wash your hands. And, you'd need multiple sensors so you could encompass things like the kitchen and other bathrooms. Also, consider the DW, which works much better with hot water. If you run yours on a timer so it runs at night after you go to bed, it may give a poor wash cycle, or, it will use its internal heaters to bring the water up to temp (if it has them and is turned on), which is likely more expensive.
  11. Gary Swart

    Gary Swart In the Trades

    Messages:
    7,302
    Location:
    Yakima WA
    FWIW, I have a recirculating system and I run it 24/7. My reasoning is that since there are times when I may want hot water at unusual times, and the small amount of power used is worth the convenience.
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