Low cold water pressure upstairs

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by Joe Mayer, Jul 18, 2020.

  1. Joe Mayer

    Joe Mayer New Member

    Joined:
    Jul 18, 2020
    Location:
    Richmond, Virginia
    Great minds,

    I have lived in my 119 year old house for 20 years. During all of this time, I have experienced good water pressure (hot and cold) downstairs. Upstairs, although I have acceptable hot water pressure, I have always had very poor cold water pressure. For example, I take a shower with the hot tap 1/4 open and the cold tap wide open. Still, it’s an effort just to wash the shampoo out of my hair. (And yes, I have removed the water restrictor from shower head.)

    It’s just my brother and me. We do not have a lot of water usage. In fact, we try not to shower At the same time or if the washer, dishwasher, or garden hose is running. I am on city water. I just measured the pressure to be 45 psi at sillcock. It’s not a big house. All of the plumbing fixtures are within 20 feet of the main shutoff valve. I suspect that the water loses most of its pressure in the rise to upstairs. I assume my hot water pressure is better because the hot water tank keeps that water under pressure and acts as reserve.

    In recent years, as part of other projects, I have replaced all of my supply lines (starting with and including the shutoff valve in the basement.). All were 40 to 60 year old 1/2 inch copper. I ran 3/4 inch pex from the household shut off valve to a cold water manifold with 1/2 inch pex to each room, except as discussed below. For the hot water, I ran 3/4 inch pex from the shutoff to the water heater and continued with 3/4 back to the manifold. I also ran 3/4 pex directly from the water heater about 10 feet to a 3/4 cpvc line to a new upstairs bathroom and laundry room. (The increase from the old 1/2 copper to 3/4 pex gave a little improvement.) The other upstairs bathroom is fed by 1/2 pex from the manifolds (hot and cold) but the last 10 feet are old 1/2 copper. (The switch from 1/2 copper to 1/2 pex made matters a little worse) All in all, the switch from 1/2 copper to 1/2 pex caused a moderate decrease in pressure throughout the house.

    What is the easiest way to increase my cold water pressure upstairs? I could increase my pipe sizes, but the last 10 feet under each bathroom would require some effort because they are only accessible through ceilings. Should I install a pump? Or should I add some sort of holding tank (as the water heater seems to help with the hot water pressure)? Thank you for any suggestions!
     
  2. Jeff H Young

    Jeff H Young In the Trades

    Joined:
    Feb 27, 2020
    Location:
    92346
    45 psi is perfect in my opinion many prefer more so its not a pressure problem its a volume problem caused by a restriction some where you gotta figure out and fix that could be angle stops are plugged up some existing rusted gal pipe but whatever figure it out or repipe it to solve
     
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  4. Reach4

    Reach4 Well-Known Member

    Joined:
    Sep 25, 2013
    Location:
    IL
    Measure the pressure at the sillcock with the tub running full cold.
    Measure the pressure at the drain valve of the WH or the hot laundry tap with the tub running full hot.
    Measure the pressure at the cold laundry tap with a tub running full cold.

    There are adapters that could let you adapt an aerator thread, if you have a removable aerator, to the upstairs lavatory faucet, to help measure pressure up there.

    Do you see much pressure drop? The point is to see where the pressure drops occur.

    And here is a temporary workaround: if you don't run out of hot water, turn the WH temperature down. That way you need less cold.
     
    Last edited: Jul 18, 2020
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  5. Bannerman

    Bannerman Well-Known Member

    Joined:
    Mar 19, 2014
    Location:
    Ontario, Canada
    A water heater is not a pump nor is it a pressure tank so the WH will not increase pressure. The same water pressure entering the home is the same pressure entering the WH and will be the same pressure exiting the WH and flowing to your hot faucets.

    Although cold water will expand when heated which under certain circumstances may raise your home's entire (both hot and cold) system pressure above the incoming municipal pressure when there is no water usage, that extra pressure, if any, will be reduced when any faucet is opened as the entire system will then equalize to the municipal supply pressure.

    As both hot and cold lines rise the same distance to the upper level, the rise to the upper level is not the cause of the pressure disparity. It then seems there is a flow restriction of some type within the cold line(s) feeding the upper level fixtures.

    1/2" PEX has a smaller internal diameter compared to 1/2" copper. Unless the original 1/2" copper pipes were partially blocked with scale or other debris, by replacing the 1/2" copper lines with 1/2" PEX, the flow rate will have actually been reduced. Any flow reduction will have been further worsened by any PEX fittings installed internally into the PEX lines.
     
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  6. Jeff H Young

    Jeff H Young In the Trades

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    Feb 27, 2020
    Location:
    92346
    1/2 inch pex fittings are kinda small . sounds like your system is undersized. I run 3/4 copper to each bathroomif its just a half bath then Ill probebly just run 1/2 inch hot to the lav. a lot of people go cheap and small but save a lot but dosent always work out. just gotta go through the leg work figuring out if there is blockage or a section of old galvie pipe
     
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  7. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Joined:
    Sep 2, 2004
    Occupation:
    Retired Systems engineer for defense industry.
    Location:
    New England
    Pressure changes due to altitude will affect any supply, so will not be different between the hot and cold.

    If I had to guess, my guess is that your old house has some sections (maybe all?) of its plumbing done in galvanized. Or, there are at least some sections done that way, maybe even the main line from the street. TO resolve your problem will probably require a repiping, maybe back to the street.

    You could do a test at the silcock...get a big bucket, run the water for a minute and measure how much volume there is.

    Do the same thing in the shower. Run pure hot (sounds like you have a two-handle, with no anti-scald tech) for a minute and measure how much water. THen repeat doing all cold. In theory, they should be identical, or really close to the same.

    Pressure and volume are related, but people often equate loss of volume to loss of pressure, and that's not the way it works. If your pipes can't flow the volume you seek, it isn't always a loss of pressure.
     
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  8. Jeff H Young

    Jeff H Young In the Trades

    Joined:
    Feb 27, 2020
    Location:
    92346
    Good explanation jadnashua! 119 yearold house sometimes there are mystories how things were done.
     
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