Space issue between mixing valve and tub spout

[Brandon in VA]

I am roughing in the plumbing for a bathroom remodel and have run into an issue. The valve inlets sit very far back on the back of the valve (center is only 1" from back wall as installed in pic). When I go to connect the drop ear for the tub spout I don't have enough room to bend a short run of pex from the bottom of the valve to the drop ear because of the difference in depths of install. I started off thinking I would use two 90 degree elbows from the valve so that the line came forward and then dropped right in front of the drop ear brace, but in that setup the second elbow came too far forward. So I created the monster in this picture (the white pex at the bottom). After reading more, though, seems like this setup could create a backflow issue that could cause water to come back through the shower line when I turn on the tub. I haven't tested that yet. I'm thinking of two potential remedies, 1) setting the tub spout drop ear on a 1x4 brace at the very back of the recess so I could drop almost straight down from the valve to the drop ear with pex and get a longer nipple (it's now measured so that I'll have a 2" nipple that extends 7/16" through the finished wall), or 2) moving the tub valve brace closer to the front of the wall, using the two 90 degree elbow setup I mentioned above and getting a shorter nipple (I don't think I can get much shorter). Also, you'll notice the sharkbite shutoff valves installed. They were originally installed because I had a leaky valve and it was getting late in the day (that's fixed) and I planned on taking those out and redoing the Pex in those runs, but we're also considering putting in a wet bar on the other side of that wall so now I'm thinking I might leave those in case we would tap the lines for that. The valve is a Kohler K-11748. Any advice?

 

[MKS]

Make sure the valve is located correctly, finished wall. 1x4 blocking for support in my limited experience.
Then do it in copper. You could add capped tees for future use.

 

[Sponsor]

 

[hj]

You CANNOT even use a short straight section of PEX between the spout and the valve. Those 90s would create so much restriction that the shower would probably run at half force every time the tub was used.

 

[Brandon in VA]

OK, I think I got it. So in addition to the 90s creating an issue I should avoid pex altogether between the valve and the spout? Is that because the inside diameter of the pex is too small or is there some other reason? I'm as confident as I'll ever be that the valve position is good relative to the finished wall, so sounds like the best resolution is copper from the valve down to the spout elbow braced against a 1 x 4?

 

[Terry]

Yes, any size restriction will force water upward to the shower head.

 

[Brandon in VA]

Hmm...that isn't my valve and the instructions for my valve don't make a mention of requiring galvanized/copper at all. Neither here nor there now but would have been good to include for newbies like me. Thanks for the information!

 

[Plumber69]

Running copper to the spout and shower head is the best way to do it. As soon as I get to a job I measure my setup and make it in the back of my van in about 20 mins. Cut my backing and screw it in. Then connect my hot and cold..... done

 

[hj]

They DO indirectly tell you to use copper or steel piping. There is a notation on the installation guide that states the top and bottom connecttions are for 1/2" threaded or 5/8" o.d. copper. Nothing about PEX or any other material.

 

[MKS]

I had a quick look at the 2015 installation guide and it seems they eliminated or I could not find the important information, use only copper or galvanized for the outlets, like Terry posted and HJ referred to.
Maybe improved instructions...

 

[Flapper]

Could you also use CPVC?

 

[Brandon in VA]

OK, so whatever the issue with instructions its very clear I need to use copper for the tub spout, which I'll do. I think I have that figured out. I would REALLY like to avoid running copper to the shower head if I can because that outlet it is not nearly as accessible to change as the tub spout. I understood the backflow issue to be caused by differential pressure between the tub and the shower, so if I have the larger tub spout in copper with no elbows am I okay to leave the PEX in the shower connection?

 

[Jadnashua]

The showerhead can remain in PEX as long as you have full diameter copper piping to the tub spout (unless the valve itself has an INTERNAL diverter...IOW, not in the tub spout).

 

[MKS]

What ever solution you choose test it before closing it up. Install tub spout and shower head. Catch with bucket to your satisfaction.

 

[Brandon in VA]

The showerhead can remain in PEX as long as you have full diameter copper piping to the tub spout (unless the valve itself has an INTERNAL diverter...IOW, not in the tub spout).

Uh oh. The diverter is in the valve. Why does this make a difference?

 

[Brandon in VA]

Could you also use CPVC?

If the issue is a smaller inside diameter on pex then I think you'd have the same issue with CPVC. Besides, I'm knee deep in PEX and copper right now, not sure I want to throw a third type of pipe into the mix if there's no significant upside.

 

[Brandon in VA]

I contacted the horse (Kohler) and they said for my valve PEX was okay from the valve to the shower, but definitely copper/steel to the tub. I'm going to run with and of course test everything before the walls are closed. Thanks everyone for your input, your experience and assistance is greatly appreciated.

 

[Terry]

We never used to have the issue of water making it's way to the shower head before the newer piping systems were added.
CPVC and PEX have a smaller diameter, thus less flow. Any restriction to the tub spout will force water upward.
Originally, all tubs were done in pipe nipples, (full sized) and copper (full sized)

The smaller lines are fine for shower heads.

 

[Jadnashua]

A typical tub spout with a diverter in it gets the flow rather than the shower head because it doesn't have the restrictions and the height to overcome (about 0.43#/ft elevation change is all it takes). All the diverter in the spout does is stop (most) of the water flowing out there, and as a result, it goes out the only other way - up to the showerhead. If you have an actual diverter valve (rather than the 'stop' valve in the tub spout), it should cut the flow off to one or the other location, but without knowing exactly how it works inside...it might just be similar to the tub spout - IOW, it may not actually shut off the outlet to the showerhead, and you'd have the same issue as if it were done in the spout. An actual working diverter would shut one port off when it opened the other, which is not how a tub spout diverter works - when using the tub, BOTH ports are open at the same time...there, restrictions are critical for proper operation.

 

[Brandon in VA]

A typical tub spout with a diverter in it gets the flow rather than the shower head because it doesn't have the restrictions and the height to overcome (about 0.43#/ft elevation change is all it takes). All the diverter in the spout does is stop (most) of the water flowing out there, and as a result, it goes out the only other way - up to the showerhead. If you have an actual diverter valve (rather than the 'stop' valve in the tub spout), it should cut the flow off to one or the other location, but without knowing exactly how it works inside...it might just be similar to the tub spout - IOW, it may not actually shut off the outlet to the showerhead, and you'd have the same issue as if it were done in the spout. An actual working diverter would shut one port off when it opened the other, which is not how a tub spout diverter works - when using the tub, BOTH ports are open at the same time...there, restrictions are critical for proper operation.

OK, got it. I can't say for sure but based on the discussion in the install manual (it says the bath spout is "Primary" flow) and the location of the diverter mechanism (towards the bottom of the valve near the tub outlet) I suspect it doesn't work much differently than a tub stop valve. Thanks for the explanation.

 

[Brandon in VA]

All installed and tested, pressure/flow is good, no backflow issues, and no leaks. I was able to solve my issue of too little space in the back of the recess by using a different type of elbow to the tub spout that sits on top of the brace and screws in below the nipple opening instead of on the sides. Considering I had never soldered a pipe or heard of pex a month ago this is a victory. Now on to the next battle in the floor. Thanks again for everyone's advice and patience.