Shower - Plumbing Moen 3/4 valves with 1/2 inch water supply

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Svierregger

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We are renovating a shower with only two fixtures - a 2.5 gpm +- Moen Velocity rain shower head and a 2.5 gpm bar-mounted hand held spray. 3/4 inch water lines run to within about 10 feet of the shower, then step down to 1/2 inch hot and cold to the shower. We are using Moen 3371 3/4 thermostatic valve and two 3/4 3600 volume control valves.

Question 1 - Moen suggests running 3/4 copper between the thermostatic output and inputs of volume controls. I noticed my plumber used 1/2 copper instead. We have to do some additional work in the wall so he can switch the 1/2 with 3/4 between the valves, but he said he doesn't feel it is necessary. It's hard for me to tell if Moen's recommendation for piping between valves is based the assumption that 3/4 is coming into the thermostatic valve, or if it is a general recommendation when 3/4 valves are used.

Question 2 - We have our valves stacked with thermostatic on bottom, then shower volume control, then hand held volume control. In the wall this leads to a number of 90's in the plumbing, the most for the shower head. Moen recommends minimizing the 90's after the volume control but they don't specify how many is too many. Currently there are two 90's and a T to get from the thermostatic to the shower head volume control, and four 90's and a 45 to get from the volume control to the shower head. The plumber is not concerned, but at this point in our home renovation I have learned to be most concerned when my contractors are least concerned.

A picture of the plumbing layout is attached.

Thanks for any feedback you can provide.

NOTE: the shower is to be a steam shower, so that is a steam line, not a tub spigot below the thermostatic valve.

moen-3371-parts-1.jpg


moen-3371-parts-2.jpg


moen-3371-valve.jpg
 

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Dj2

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I'd do as the instructions suggest. You can tell the plumber that you will pay for the difference in the cost of the 3/4 pipe and fittings.

 
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Jadnashua

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I think that Moen is assuming that if you bought 3/4" valves, you'd have fed it with 3/4" supply lines, so restrictions after would not be good. With 1/2" coming in and 10' from the 3/4" supply line, I don't think you'd gain anything. But, at this point, it is cheap to make it 3/4". I'd have considered making the whole run 3/4" to the valves.
 
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