Uponor PEX for his & hers shower - 1/2 or 3/4

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Darel Matthews

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I am going to be completely redoing my 2nd floor shower, and installing his & hers shower heads on separate valves.

The basic layout will be, shower valve 1 on 30" wall, tub spout with diverter 7" below. Both shower heads will be on the 60" wall, 20" in from either end, so a long run to the head from this valve. Valve and head #2 will both be on the 60" wall, 20" in from the corner, obviously no tub spout.

I have 1/2 copper feeding the current single valve in the existing shower.

Plan is to tee off the existing copper lines to feed both valves.

New shower valves have 1/2MNPT connections.

Question is, what size should I use for the new lines? I can easily stick with 1/2 but I worry I may lose flow. I can adapt up to 3/4, but the existing feed lines and the shower valves are still a restriction, and I worry about not having the requisite resistance to keep the tub spout functioning correctly.

I am getting 4.7gpm to the current shower head and 4.3 when I flush the toilet and run a sink, so right now I have plenty of flow for the two shower heads I chose. But will all the added restrictions cause issues and would running 3/4 (or a combo of 1/2 and 3/4) mitigate any of this? Also, I understand the issues with running PEX to the tub spout, but Uponor is less restrictive, plus I have the long curved run to the shower head off valve #1, so do you think I can get away with PEX on the tub spout?

I am planning on piping everything in and trying it out, and if I need to add a booster pump in the basement I can, but I'd prefer not to.

Or am I just really overthinking this?

Thanks,
Darel
 

Terry

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You can not run any kind of PEX to a tub spout that uses a diverter. I've had to cut walls on other peoples work to fix those things.
Every valve manufacturer warns against it.

pex-to-copper-fitting.jpg


Uponor PEX fitting compared to copper pipe.

moen-tub-spout-instruction.jpg


Moen

k-304-r02.jpg


Kohler
 
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Jadnashua

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In the US, showerheads must adhere to a 2.5gpm max. If you have 4.7gpm available and less, you may not get the full acceleration from the nozzles, they'll be more like rain shower heads if your shower head selection is actually near that max. You want your supply capacity to exceed the shower head's output to achieve any acceleration. A shower head's nozzles only accelerate the water flow if they are restricting the flow, otherwise, it just flows through without acceleration which people often mistake for loss of pressure (it's the velocity increase that gives you the forceful shower spray - the head does not increase the supply pressure). Bernoulli principle describes the affect...

Feeding the valves with 3/4" pex will allow more volume than using 1/2" pex and is closer to 1/2" copper (slightly larger ID with that pex vs 1/2" which is smaller than 1/2" copper). 1/2" pex from the valve to the head will work fine.
 

Darel Matthews

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In the US, showerheads must adhere to a 2.5gpm max. If you have 4.7gpm available and less, you may not get the full acceleration from the nozzles, they'll be more like rain shower heads if your shower head selection is actually near that max. You want your supply capacity to exceed the shower head's output to achieve any acceleration. A shower head's nozzles only accelerate the water flow if they are restricting the flow, otherwise, it just flows through without acceleration which people often mistake for loss of pressure (it's the velocity increase that gives you the forceful shower spray - the head does not increase the supply pressure). Bernoulli principle describes the affect...

Feeding the valves with 3/4" pex will allow more volume than using 1/2" pex and is closer to 1/2" copper (slightly larger ID with that pex vs 1/2" which is smaller than 1/2" copper). 1/2" pex from the valve to the head will work fine.

The heads I chose are 1.78 gpm and they are rainfall style heads....does that make a difference? I figured even at the minimum 4.3 I have (during toilet flush) I'm still OK.
 

Jadnashua

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Rainfall heads, with the numerous outlets, aren't intended to accelerate the water, so probably won't be impacted with 1/2" in your case. IOW, the velocity of the water won't change (much, if at all), but you might notice a slight decrease in volume when someone flushes a toilet and your indicated flow rate is expressed into the system. It becomes much more critical when you're using a conventional head, and are expecting the force out to be high. There, if it's starved on the supply side, there's nothing to speed it up in the nozzle - rain shower heads don't speed the flow up, but still have a flow restrictor in them to meet the federal standards, so there could be just less water coming out - sort of like my hose example without a nozzle except with a rain shower head, it gets divided into multiple streams.
 
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