(206) 949-5683, Top Rated Plumber, Seattle
Results 1 to 11 of 11

Thread: Why one inch PEX?

  1. #1
    DIY Junior Member neosec's Avatar
    Join Date
    Jan 2011
    Location
    PA
    Posts
    2

    Default Why one inch PEX?

    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. #2
    In the Trades Gary Swart's Avatar
    Join Date
    Sep 2004
    Location
    Yakima WA
    Posts
    7,246

    Default

    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 by Gary Swart; 01-19-2011 at 01:19 AM.

  3. #3
    Moderator & Master Plumber hj's Avatar
    Join Date
    Aug 2004
    Location
    Cave Creek, Arizona
    Posts
    25,624

    Default

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

  4. #4
    Retired Defense Industry Engineer jadnashua's Avatar
    Join Date
    Sep 2004
    Location
    New England
    Posts
    21,388

    Default

    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.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  5. #5
    DIY Junior Member neosec's Avatar
    Join Date
    Jan 2011
    Location
    PA
    Posts
    2

    Default Thanks

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

  6. #6
    Plumber jimbo's Avatar
    Join Date
    Aug 2004
    Location
    San Diego
    Posts
    9,001

    Default

    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. #7
    Retired Defense Industry Engineer jadnashua's Avatar
    Join Date
    Sep 2004
    Location
    New England
    Posts
    21,388

    Default

    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.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  8. #8
    Moderator & Master Plumber hj's Avatar
    Join Date
    Aug 2004
    Location
    Cave Creek, Arizona
    Posts
    25,624

    Default

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

  9. #9
    DIY Senior Member DavidTu's Avatar
    Join Date
    Dec 2009
    Location
    Seattle, WA
    Posts
    229

    Default

    Any opinions/experience with Uponor's record system that uses motion sensors to run the recirc?

  10. #10
    Retired Defense Industry Engineer jadnashua's Avatar
    Join Date
    Sep 2004
    Location
    New England
    Posts
    21,388

    Default

    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.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  11. #11
    In the Trades Gary Swart's Avatar
    Join Date
    Sep 2004
    Location
    Yakima WA
    Posts
    7,246

    Default

    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.

Similar Threads

  1. Another 4-Inch versus 8-Inch Sink Drill Question
    By RonnyK in forum Remodel Forum & Blog
    Replies: 9
    Last Post: 01-27-2009, 09:45 AM
  2. Cable tool or bore drill? 5 inch pvc or 4 inch steel?
    By Barnes in forum Pumps and Tanks Well Forum & Blog
    Replies: 5
    Last Post: 05-16-2008, 05:48 AM
  3. Cutting 2 inch and 3 inch copper pipe
    By JohnO in forum Plumbing Forum, Professional & DIY Advice, Tips & Tricks
    Replies: 2
    Last Post: 11-09-2006, 10:35 AM
  4. Problem flowing 4 inch PVC into 3 inch cast iron?
    By skip in forum Plumbing Forum, Professional & DIY Advice, Tips & Tricks
    Replies: 8
    Last Post: 08-26-2005, 07:03 AM

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •