Supply to 3/4" valve?

Discussion in 'Plumbing Forum, Professional & DIY Advice, Tips & ' started by fjordrr, Jan 13, 2009.

  1. fjordrr

    fjordrr New Member

    Messages:
    20
    Location:
    Washington
    Well now I'm tackling my other unfinished bathroom. It has the usual 1/2" supply lines roughed in to the shower area. I bought 3/4" valves which will go to 1/2" showerheads.

    My question is: do I just convert ONCE from 1/2" to 3/4" supply lines before the 1st valve (thermostatic mixer) continuing to use 3/4" supply for the rest or do I run 1/2" supply between each 3/4" valve?

    So just to outline the full scenario, we have:

    A. 1/2" rough-in supplies ->
    B. 3/4" thermostatic mixer ->
    C. 3/4" volume control ->
    D. 3/4" diverter ->
    E. 1/2" showerheads.

    Thanks for any help!!
  2. Basement_Lurker

    Basement_Lurker One who lurks

    Messages:
    668
    Location:
    Victoria, BC
    Well, since your supply is already 1/2", having those valves at 3/4" is a total waste. It really won't make any difference how you do it since the pressure/volume is already fixed at 1/2" specs. I suggest that you just keep it simple and reduce all fixtures to 1/2".
  3. fjordrr

    fjordrr New Member

    Messages:
    20
    Location:
    Washington
    Well that's what we were all thinking, but per Grohe's shower design manual:

    "It is not necessary to have a 3/4" supply line to use a 3/4" valve.
    A 1/2" supply line plumbed into a 3/4" valve will still effectively increase water flow, but a 3/4" supply line is preferred. "

    I actually went with Hans-Grohe valves, but their phone tech support told me to get 3/4" valves also.
  4. suncoasttubs

    suncoasttubs New Member

    Messages:
    3
    Location:
    Canada
    Hmmmm

    I'd like to read the physics behind the idea that a 3/4 valve supplied by 1/2 lines would increase flow over a 1/2 inch valve given the same line pressure.
    No I mean it. Really, I'm curious how this could be explained by an engineer so I could understand the principal involved.
  5. Furd

    Furd Engineer

    Messages:
    446
    Location:
    Wet side of Washington State
    Would a retired engineer do?

    The typical 1/2 inch bath faucet has passages with an equivalent diameter of 1/4 inch or less. A 3/4 inch bath faucet would have larger passages but most likely still less than the interior diameter of the 1/2 inch pipe supplying the faucet.
  6. C NUMB

    C NUMB Plumbing Contractor

    Messages:
    135
    Location:
    NPR, FL
    What is (D) 3/4" diverter for????

    The 1/2 will work but the there will be some pressure loss if both shower heads are used.

    How are use setting up the shower, location of valve/volume controls/heads??
  7. fjordrr

    fjordrr New Member

    Messages:
    20
    Location:
    Washington
    D) - the diverter - will operate 3 "functions" - a handshower, showerhead, & 2 body sprays. It can do each function separately, or any 2 at one time.

    The 3 valves (B,C, D) will be vertically on one wall, one on top of each other. This wall will also have the hand shower.

    The 2 body sprays will be on the other adjacent wall, and the rain shower head will be mounted in the ceiling.
  8. C NUMB

    C NUMB Plumbing Contractor

    Messages:
    135
    Location:
    NPR, FL
    I think you will be disappointed with shower if you cannot get 3/4" hot and cold feed to the main valve with that much going on in the shower. We have done many Grohe systems and if it is not plumbed right it will not function. Instead of that diverter, I would opt for 3 more volume controls.
  9. zxed

    zxed New Member

    Messages:
    61
    Location:
    California
    i had the same issue...

    my bathrooms incoming was 1/2" i wanted to build a kohler performance shower

    i was going to convert the 1/2" to 3/4" as early as possible.

    my kohler thermostatic pressure balancing valve was 3/4" and all the wall tile body sprays were 1/2"... i was confused in the begining...

    is converting 1/2" into 3/4" a total waste? no its not... but is it worth the $ spent? :) no its not.

    a proper 3/4" setup will give you 18ish gpm
    1/2" gives you 8ish gpm
    1/2" converted to 3/4" give you 10ish gpm...

    all asuming that you have good water pressure.

    why does all this matter?
    usually, a shower components needs 2.5gpm
    so having 1/2" as your supply., will mean you can run a maximum of 3 shower components at one time., this could be 3 body sprayrs., or 2 body sprays and 1 hand shower, or 1 body spray, 1 handshower and 1 overhead shower...

    my setup in shower parts if i had gone with the 3/4" convert was costing $1750... by coming to my senses and working with what i had,, which is 1/2"... i paid $1050 for the shower parts . :)


    return the 3/4" valves,. get 1/2" valves., ...
  10. fjordrr

    fjordrr New Member

    Messages:
    20
    Location:
    Washington
    Thanks for the continued info. Since I can only run a max of 2 functions at one time (diverter's limit), they will be limited to 5 gpm total for the hand shower & ceiling rainhead together, and 4.5 gpm for either showerhead plus the 2 body sprays together. So I am OK there.

    I bought the valves & trim a while back, so I am an owner - have to work with the 3/4".
    Last edited: Jan 13, 2009
  11. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,522
    Location:
    Cave Creek, Arizona
    pipes

    The 1/2" lines are probably a lot larger than the openings in the 3/4" valves. For simplicity's sake, increase to 3/4" at the valve, connect all the 3/4" stuff together with 3/4" brass or copper, then reduce going to the shower head(s).
  12. fjordrr

    fjordrr New Member

    Messages:
    20
    Location:
    Washington
    Thank you very much! :) Work is beginning today.
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