1/2 supply lines to a 3/4 inch transfer valve, multiple options

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mgd150

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Looking for some advice on what the best setup will be for my scenario.

I want to use a Kohler 3/4 inch inlet 3 way transfer valve to switch between a tub spout, a handheld shower, and a rain head. I'd like to be able to use the handheld and rain head at the same time, each of them are 2.5 gpm.
The transfer valve is 3/4 in and 1/2 out.

Problem: I have 1/2 inch supply lines, so at some point I need to convert to 3/4 to use the transfer valve.

My question: is it better to

1. convert from 1/2 to 3/4 into the mixer valve - Kohler HiFlow PB valve, 13 gpm out, K-2971-KS-NA, then continue 3/4 to the transfer valve (could also use 3/4 thermostatic valve here if it would handle the 1/2 to 3/4 conversion better)

or

2. go 1/2 into the mixer valve - Kohler thermostatic 1/2 inch, 7 gpm out, and convert 1/2 to 3/4 to the transfer valve

The only other solution would be to ditch the transfer valve and use individual volume controls for each output, but my wife isn't interested in having that many knobs on the wall. She barely wanted a third knob for the thermostatic stack.
 

mgd150

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For illustration, attached a picture of what I'd like to do.
 

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Reach4

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Feeding 3/4 tempered water, from a nearby 3/4 inch thermostatic mixing valve, into the hot of the mixing valve from your drawing would give better flow than using tempered water via the long 1/2 inch line. The 1/2 inch line would have to be supplied with hot instead of tempered water. This presumes the WH is supplying water at higher temperature.

This arrangement would give hot water faster than running 3/4 from the WH. Once hot water arrives, then some cold will contribute to the gpm.

Yep, costs more, and you might have to take special action to make sure the lavatory hot is tempered water also.
 

mgd150

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Feeding 3/4 tempered water, from a nearby 3/4 inch thermostatic mixing valve, into the hot of the mixing valve from your drawing would give better flow than using tempered water via the long 1/2 inch line. The 1/2 inch line would have to be supplied with hot instead of tempered water. This presumes the WH is supplying water at higher temperature.

This arrangement would give hot water faster than running 3/4 from the WH. Once hot water arrives, then some cold will contribute to the gpm.

Yep, costs more, and you might have to take special action to make sure the lavatory hot is tempered water also.

Thanks for the response, bathroom is on the second floor, so unfortunately I dont think we will have access to change any of the plumbing between the WH and the bathroom, I think we're stuck with the existing 1/2 inch supply lines. That being said, will it not work the way I have it drawn up?
 

Tuttles Revenge

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Yes, you have the correct orientation of valves. Thermostatic valve supplying a transfer valve in turn supplying your outlets.

What transfer / diverter valve are you using? Does it allow 2 fixtures at once to be used? Usually it halves the flow to each.

Rainheads are often a dissapointing feature as they act like rain.. they drop water rather than spray in most cases. So they're best if used on a horizontal plane aimed straight down.
 

mgd150

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Yes, you have the correct orientation of valves. Thermostatic valve supplying a transfer valve in turn supplying your outlets.

What transfer / diverter valve are you using? Does it allow 2 fixtures at once to be used? Usually it halves the flow to each.

Rainheads are often a dissapointing feature as they act like rain.. they drop water rather than spray in most cases. So they're best if used on a horizontal plane aimed straight down.

Going to use the K-728-K-NA, which allows 2 fixtures at the same time.

Planning on doing an 18 inch bar and right angle for the rain head.

My plumber is suggesting I keep the 1/2 inch inlets to the mixing valve and adapt to 3/4 at the transfer valve. This is disappointing because the only 1/2 inch pressure balance valve is a 5 GPM out.

Looking for the highest GPM, I think Im going go to with separate thermostatic and volume valves. The 1/2 inch Kohler Thermostatic is about 11 GPM out, the volume valve is 10 GPM. This should also fill my tub faster.
 

Tuttles Revenge

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1/2" is going to be a limiting factor. How much volume will your tub need to fill? Ive been bitten once with a big soaking tub that we installed a 1/2 shower valve.. took 15 min to fill. Once I swapped to a 3/4 it took 5.

I don't know of any functional downside to installing the K-2971-KS-NA with half inch feeding it. I don't have one in stock to look, but a half inch valve is going to have 3/8 porting.. while a 3/4 valve will likely have 1/2 porting..

I lied.. I do have that kohler valve on the shelf and it has nearly 3/4" porting.. bigger than the Hansgrohe does... I can't see any downside of feeding that valve with 1/2 and getting zero restriction.. OK.. way way less restriction from the shower valve.. Spend the money on the bigger valve.
 

wwhitney

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FWIW, Delta says their R10000-UNBXHF single port rough-in with a 17T dual function (temperature and volume) thermostatic cartridge will flow 7.6 gpm at 40 PSI, 9.4 gpm at 60 PSI, and 10.9 gpm at 80 PSI.

https://www.deltafaucet.com/sites/delta/files/2019-11/Delta Flow Chart 2018-06-27.pdf

Cheers, Wayne

P.S. In case it is not clear, the way overall flow is determined is like this: say your static pressure (no flow) at the shower valve would be 60 PSI, and say that you use the above valve, and that the piping between your water source and the valve would drop 20 PSI in frictional losses when flowing 7.6 gpm (jointly between the two supply lines, with the flow in the proper ratio to provide the target temperature). Then there would be 40 PSI at the valve input at 7.6 gpm, and you'd get 7.6 gpm through the system, assuming that your diverter and tub spout provide no additional frictional pressure loss.
 

mgd150

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1/2" is going to be a limiting factor. How much volume will your tub need to fill? Ive been bitten once with a big soaking tub that we installed a 1/2 shower valve.. took 15 min to fill. Once I swapped to a 3/4 it took 5.

I don't know of any functional downside to installing the K-2971-KS-NA with half inch feeding it. I don't have one in stock to look, but a half inch valve is going to have 3/8 porting.. while a 3/4 valve will likely have 1/2 porting..

I lied.. I do have that kohler valve on the shelf and it has nearly 3/4" porting.. bigger than the Hansgrohe does... I can't see any downside of feeding that valve with 1/2 and getting zero restriction.. OK.. way way less restriction from the shower valve.. Spend the money on the bigger valve.

Thanks for the feedback everyone, I was mainly looking to double check that there would be any functionality issues with feeding the 1/2 inch supply. I know its not ideal, but I'm just not comfortable with the 5 gpm that the 1/2 inch pressure balanced valve will output.
 
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