Low pressure from PEX manifold

Discussion in 'Plumbing Forum, Professional & DIY Advice, Tips & ' started by shayniferd, Nov 6, 2009.

  1. shayniferd

    shayniferd New Member

    Messages:
    6
    I just installed a PEX manifold system and have significantly lower pressure than I did with my galvanized system. The copper pipe from the street is 3/4, which I transitioned to 3/4 PEX. I ran straight to the water heater and have less than three feet of pipe from the water heater to a five port manifold and also about three feet of water from the T to the water heater to a ten port cold water manifold. There were no leaks that I could find, so i don't think I'm losing pressure there.
    What could cause a loss in pressure like this?
    Thanks
  2. Terry

    Terry Administrator Staff Member

    Messages:
    15,016
    Location:
    Bothell, Washington
    3/4" PEX is smaller then copper sizing.
    How many bathrooms do you have?
  3. shayniferd

    shayniferd New Member

    Messages:
    6
    Two full baths.
    In the previous system, the copper transitioned to galzanized as it passed the water heater. How is the diameter of 3/4 galvanized compared to 3/4 PEX?
    The faucets that are closer to the manifold have much better pressure than the ones furthest away if that helps ID the problem.
  4. Terry

    Terry Administrator Staff Member

    Messages:
    15,016
    Location:
    Bothell, Washington
  5. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,025
    Location:
    New England
    What size is the manifold and the pipes leaving it?

    Galvanized could be quite small ID after a long time. It's hard to compare old stuff with new pipe. Could be clean, could be the opening of a soda straw or smaller.
  6. shayniferd

    shayniferd New Member

    Messages:
    6
    I thought I should have one inch from the meter as well, but it is definitely 3/4. I have enough copper to run it to the water heater and just up to the manifolds. I'll try that and see if it helps.
    Thanks
  7. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,653
    Location:
    Cave Creek, Arizona
    pipe

    3/4" PEX has only slightly higher capacity than 1/2" copper. What size are the lines from the manifold to the faucets. If they are small, or overly long, that will be the most likely source of your poor pressure.
  8. shayniferd

    shayniferd New Member

    Messages:
    6
    From the manifolds to the faucets it is 1/2 PEX. The shorter lines were OK, but the longer ones were terrible.
    I replaced the 3/4 PEX with 3/4 Copper and that has helped. The shorter lines now have adequate pressure. I ran 3/4 PEX on my longest run, to the kitchen, but the pressure is sill low. It's about a 30 foot span. I guess I'll have to go 3/4 copper there too.....
    I've learned a lot with this if nothing else. I plan on building a house in the next few yeas and this is valuable information.
    Thanks to all those who replied.
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