Pex with thermostatic valve/volume valves

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by tomtbone, Jul 11, 2010.

  1. tomtbone

    tomtbone New Member

    Messages:
    28
    Location:
    tomtbone in Boston
    I have heard that I should not use pex between a shower valve and tub spout because of resistance. I will be using a 3/4" thermostatic valve with separate volume controls for the tub and multiple shower heads; all 3/4".

    Having volume controls for everything including the tub, anyone see a problem using 3/4" PEx for everything and no copper as long as its all strapped down?
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,129
    Location:
    New England
    You'll lose some of the volume capability of the valve if you use pex. Often, they specifically say not to use it to interconnect pieces. Using it as a supply also means you won't get the maximum volume you could have. in a traditional setup, using 1/2" pex, with a divertor spout, it will back up into the shower. Since most stub spouts are 1/2", using pex to it would be a problem. I'd use copper after the valve for all connections. This will also mean that you can anchor it well.
  3. tomtbone

    tomtbone New Member

    Messages:
    28
    Location:
    tomtbone in Boston
    I am not using a traditional setup however with a diverter. The tub spout is basically plumbed like another showerhead, it has its own volume control (on/off). I suppose I could always use 1/2" copper to go down to the tub spout, but I could also use Pex drop ear elbows screwed into 2x4's. and that would be just as solid right?
  4. nhmaster3015

    nhmaster3015 Master Plumber

    Messages:
    836
    Location:
    The granite state
    The reason for not using it between the valve and the spout is because the added restriction can force water up through the shower head when you are filling the tub. The mixing valve should have no effect one way or the other. If you don't mind the shower head dribbling than go for it.
  5. jimbo

    jimbo Plumber

    Messages:
    8,997
    Location:
    San Diego
    The issues you heard about involve using 1/2" PEX on a 1/2" shower valve. I suspect the same issue would apply to using 3/4" PEX on a 3/4" valve. Consider using copper for the drop to the spout. And remember in terms of your overall plan, that 3/4" PEX is more or less equivalent to 1/2" copper.
  6. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,811
    Location:
    Cave Creek, Arizona
    You do NOT have the same dynamics in your design that a diverter spout would. ALL of your devices will have a positive shutoff valve in the line going to them so it makes no difference WHAT you use, or the size, to any of them, including the spout. A bigger issue, if the thermostatic valve has an on/off function would be that you should NEVER have all the volume control valves off at the same time. Even though the valve should have "check stops", you could leave the valve turned on, and stop the flow with the volume controls, which could create a "cross over/backflow" situation between the hot and cold systems.
  7. tomtbone

    tomtbone New Member

    Messages:
    28
    Location:
    tomtbone in Boston
    What I have is a Kohler Thermostatic valve, with no volume control built in. IT is meant to only control the temperature.
    http://www.us.kohler.com/onlinecatalog/pdf/1041158_1.pdf
  8. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,129
    Location:
    New England
    Read the installation instructions very carefully. Many of them must have the water going INTO them turned off, i.e., not have the water OUT of them stopped. This is why most people use a multiport divertor valve rather than multiple stops. If it isn't obvious from the instructions (it may only be one line or word burried somewhere), I'd call the manufacturer's tech support line and specifically get their okay for your installation plan...
  9. tomtbone

    tomtbone New Member

    Messages:
    28
    Location:
    tomtbone in Boston
    This is what it says in the directions:

    The K-669 and K-679 thermostatic mixing valves do not contain an integral volume control/shut-off valve. You must install a separate volume control/shut-off valve (K-671 or K-681)
    downstream of any used valve outlet.

    thermo.jpg
Similar Threads: thermostatic valve/volume
Forum Title Date
Plumbing Forum, Professional & DIY Advice suppllying a 3/4" thermostatic shower valve Jun 4, 2014
Plumbing Forum, Professional & DIY Advice Please help with old Grohe Grohmix thermostatic shower faucet Nov 16, 2013
Plumbing Forum, Professional & DIY Advice kitchen faucet with thermostatic valve Sep 13, 2013
Plumbing Forum, Professional & DIY Advice Thermostatic valve for tub Jul 1, 2013
Plumbing Forum, Professional & DIY Advice Installing a Thermostatic Mixing Valve May 13, 2013

Share This Page