glav Steel to PEX bathroom remodel

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by tlt3900, Jan 7, 2013.

  1. tlt3900

    tlt3900 New Member

    Messages:
    13
    Location:
    Cypress Texas
    Hi,

    I've finally started my bathroom remodel and have mostly completed the demolition phase. I've removed everything down to the studs, including removing the existing glav steel. I'm planning on using PEX as the replacement in the Master bathroom, following it up with replacing all of the galv steel pipe I can reach in the rest of the attic.

    My question is, and I apologize if it's been asked before, is since the ID of PEX is smaller than the Galvanized pipe, I was thinking of running 3/4 inch PEX to the shower valve with a 3/4" PEX to 1/2" NPT fitting for the connection. The ID of the 1/2" PEX seems so small, I'm concerned with low flow at the shower. Any thoughts? Does this sound reasonable? The shower will consist of a hand spray, three body sprays, and a overhead rainshower.

    The overall plan is to run a hot and cold 3/4" trunk line and drop off to 1/2" for each of the vanities and toilet, with a 3/4" drop for the shower. I also have considered a small manifold, one each for the hot and cold, which I may do if the feeling is that 1/2" feed to the shower is appropriate.

    Any feedback is greatly appreciated.
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,321
    Location:
    New England
    Check the manufacturer's specs on the gpm of the things you want to run simultaneously. 3/4" pex might be too small. 1/2" pex will run one showerhead fine, but might struggle with two. You might need a 3/4" valve, then you might want to run 1" pex to it. It all comes down to the gpm demand with everything on. Without knowing that, it's all a guess which includes which valve you need.
  3. tlt3900

    tlt3900 New Member

    Messages:
    13
    Location:
    Cypress Texas
    Each of the devices by themselves has a max flow rate of 2.5 GPM. So, together the max would be 7.5 GPM if you ran all together. The connections into the control valve and the diverter valve are all 1/2 NPT so doesn't that pretty much restrict what the max flow is going to be anyway? With the 3/4" PEX I was trying to match the ID of the 1/2" connection as much as possible with the PEX.

    The diverter valve allows for all possible combinations, one device by itself or any combination of devices up to all three on at once.
  4. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,321
    Location:
    New England
    7.5gpm is exceeding the maximum velocity of the water in the pipe system for a 1/2" valve. Now, depending on how hot you like your water, you might source that amount into the valve since each of the hot and cold pipes wouldn't be at the max, but out of the valve, trying to feed 7.5gpm, I don't think you'll be satisfied. To maintain the velocity out of the spray heads, you need to provide MORE volume so you get the nozzle effect like you would on a hose. Two heads, maybe on a 1/2" valve/supply, three, I think you're pushing it too far.
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