Best way to plumb 2-way diverter and mixing valve for shower/tub?

[Lordoftheflies]

Hi.

Wondering if you all could offer suggestions as to how to plumb my shower/tub combo.

I have the Kohler 2971-k-na 3/4" inlet and outlet mixing valve. I'll be bringing up 1" PEX to the 2nd floor the entire way from the 3/4" copper main. This unit does not have a built in diverter and has only one outlet.

To switch between the tub and the shower I'll be using the Kohler 737-ks-na. This is a 3-way transfer valve but I have already configured it for 2-way operation.

The installation manual for the 2971 says to not use elbows on the outlet so I'm assuming that means I have to install the diverter above the mixing valve (which makes sense anyways).

The outlet for the bath on the diverter will be on the left (facing the valve as if you're using it). I'll be using 1/2" copper to the tub spout since both the outlet on the diverter and the tub spout pipe are 1/2".

My concerns:

1. Will I be using too many elbows from the diverter to the tub spout? One will turn down from the diverter, one will turn right to bring it back to center, then one more to turn into the drop ear. Plus I don't know if I need an additional in case the pipes block each other.

2. The 2971 mixing valve doesn't have any brass screw holes to secure it to the bracing. The only screw holes are in the plastic guard all the way in the front of the unit. That guard does seem pretty sturdy but the entire back of the unit is smooth and this is a heavy unit. It measures 3.5" from the front of the plastic guard to the rear of the unit and the guard is only 3/8" thick. Is this unit designed to be held in by the 3/4" copper piping? Since I'll be using 1" PEX which is quite stiff, I suppose it's some ok but I still don't like it. I don't understand why they didn't include some brass screw holes to secure the valve to the 2x4 bracing. In the below pic for shower only configuration (all the pics for all the configs look the same) you can clearly see the back of the unit up against the bracing. The rear face is just about 3.75" so even if I wanted to use those holes in the brace they don't line up.

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This is the only part it talks about bracing in the installation manual.

If you go to the roughing-in section this is what you see. Not very helpful.

3. Can I use 3/4" PEX from the diverter to the shower or should I use 1/2" copper?

4. Here's a quick sketch of what I'm thinking of doing. Please feel free to correct anything.

5. Here's a pic of the unit sitting on a 2x4. I was thinking maybe I could use some straps around the outlet brass but those are inset from the back of the unit.

6. Should I use long sweep copper elbows instead of short ones? I'm trying to fill a 70 gallon 66" x 32" x 22" bathtub quickly....And I want to minimize turbulence and friction.
Thanks.

 

[Lordoftheflies]

Maybe something like this?

Luckily I will have space behind the shower and leave it basically unused so I can access in the future if necessary. Otherwise this will not fit inside a 2x4 wall as others who have reviewed it online, etc. have posted.

 

[Sponsor]

 

[Terry]

I think you will fine using the 1/2" copper off the diverter for the tub spout. Similar to page six on their instructions.

 

[Lordoftheflies]

Thanks Terry. That covers #3. Any input on #1, 2, 4, 5 and 6?

Here's a quick sketch of how I think I can mount the mixing valve.

Might not need the vertical 2x4 in between the horizontal 2x4 flanking the mixing valve.

 

[Terry]

1) The two elbows are fine from the diverter. The other option they showed without the diverter was for a diverter tub spout with a twin ell. You don't have that.

2) I normally run copper a short ways from a valve so that I can strap. I don't like using PEX for that. And I don't see a reason for the 1" PEX instead of the 3/4". Can't hurt I guess.

3) you can use 3/4" PEX to the shower head. What is the flow rate of the shower head? Normally 1/2" PEX is fine for that. Most of mine are run in copper if I'm hanging the valve from the top drop ear, but in a situation like yours, I often PEX it.

4) The drawing looks good.

5) Sure, that would work. They do make a copper plated plumbers strap.

6) You can, but the standard 90's on 3/4" will work fine. I used to install a lot of the Grohe Roman Tub faucets in 3/4" and they did fill very fast.

 

[Lordoftheflies]

1. I think I can do it with 2 elbows pointed at 45 degrees to each other and just install the drop ear sideways. That way I minimize the number of elbows.

2. I'm using 1" because I bought a roll of 100' when I redid the piping in the basement so I have a lot of extra. Also, I wanted to make sure I maximized my flow and minimized my friction which is why I didn't go with 3/4" pex. I have 3/4" copper main which transitions post sediment filters to 1" pex. Btw I'm never buying a roll again. Man what a PITA it was to straighten out.

3. I removed the flow rate restrictor but it's the Purist Single Handle Rite Temp trim kit. 2.5gpm for the shower head. I think the flow and pressure should be fine with pex. I'll see what I have left over in pex and copper.

4. I think I need to adjust the 2nd one. I think I'll go with #2 without the vertical supports. I'll install some vertical cleats using 2x4 or maybe 2x6 depending on how far back I have to install it which will make the horizontal braces sturdier and a tad easier to line up.

5. Thanks I'll check those out.

6. The diverter (Kohler 737-k-na) is rated for 18gpm max out of one outlet. The mixing valve puts out 13gpm (Kohler 2971-ks-na) so I think it should be ok. 70 gallons / 13 gpm = 5.3 minutes to fill to capacity and with me in there we're probably talking only about half that time. In hindsight maybe it was a bad idea to remove the flow restrictor in the shower before actually testing it although I do like max pressure when showering.

Thanks Terry.

 

[Lordoftheflies]

One more thing I thought of - the diverter and the mixing valve may not line up in a straight shot. Is it ok to use a 45 elbow to adjust for the front/back offset? The manual does specifically say not to use an elbow.

Nm. I checked the manuals for both and it appears it will indeed be a straight shot.

 

[mgd150]

One more thing I thought of - the diverter and the mixing valve may not line up in a straight shot. Is it ok to use a 45 elbow to adjust for the front/back offset? The manual does specifically say not to use an elbow.

Nm. I checked the manuals for both and it appears it will indeed be a straight shot.

Reviving this thread, wanted to see how this turned out, I'm about to do something similar using the HiFlow Rite Temp but with the Transfer valve rather than the diverter. My only concern is that I'm running 1/2 inch copper supply lines into the mixing valve, then 3/4 from mixing valve to transfer valve, then 1/2 to each of the tub spout, handheld shower head, and rain shower head.

How is your pressure? Do you think I'll be fine running the handheld and the rain head at the same time?

 

[Lordoftheflies]

Reviving this thread, wanted to see how this turned out, I'm about to do something similar using the HiFlow Rite Temp but with the Transfer valve rather than the diverter. My only concern is that I'm running 1/2 inch copper supply lines into the mixing valve, then 3/4 from mixing valve to transfer valve, then 1/2 to each of the tub spout, handheld shower head, and rain shower head.

How is your pressure? Do you think I'll be fine running the handheld and the rain head at the same time?

With no information on the size of your house, how far away you are from the water heater, how big your incoming lines are, how big your main lines are, whether or not you have a PRV and what it's set to, if you have a filtration system and if so if you have the 20gpm high flow filters, how your pressure was in your old setup (whatever that was), what fixture you got (i.e. how big your rain shower head is) how your plumbing is......plumbed......it makes it very difficult to guess how your pressure will be. I don't think anybody can guess that with so little information.

That said, I don't think you need an extraordinary system to run a rain shower head and a handheld....But if you're on the 3rd floor and you're 120 feet from your heater and you have 1/2" pipe all the way to the heater, you may have a flow problem. Good luck!