PEX A from CPVC Shower Remodel Question

[TomV8]

Hello everyone. I am remodeling my jetted tub/shower down to the studs. I currently have 15 year old 1/2 CPVC pipes.

I will be installing a 2.5 gpm shower head with a 2.5 gpm shower wand to a Delta 3-way multi valve. The shower valve is supposed to be rated at 5.3 gpm at 40 psi, 6.5 gpm at 60 psi and 7.4 gpm at 80 psi. I currently don't know what my current actual specs are but the water flow and pressure seems pretty nice.

I am going to have to reroute the water lines since the builder has the water supply going from the wall to a roman style tub faucet. The lines are then T'd off at the faucet. The cold has three 90's zig zag around the tub with another 90 degree to run the wall. The hot only has two 90's. Then both supply lines hits another 90 to connect to the valve.

I would like to operate the shower wand and shower head at the same time so I was thinking of installing PEX A. so the flow wouldn't decrease to terribly much compared to the crimp fixtures of PEX B. I will be (should be) doing the install myself. All the 1/2 fittings are readily more available than the 3/4 fittings. I can order all the 1/2 parts from one brand and from one location, but with the 3/4 I will have to order things from a few locations, especially the 3/4 PEX A to 1/2 drop elbow. The difference in price isn't a deciding factor since this is a remodel and the difference is small since the distance is only like 5 ft per line.

The wall the shower and the pipes will be on is a non structural interior wall bumped out from the actual exterior wall. I can enough room, I can probably have the PEX tubing to directly from the floor CPVC adapter to the valves with no other fittings.

Couple of questions. Should I install 1/2 or 3/4 PEX A from the CPVC supply lines to the valves to keep a flow loss at a minimum especially since the inner diameter of 1/2 PEX is much less than the inner diameter of CPVC? Then which should I use to the shower head and shower wand drop elbow fixture? 1/2 or 3/4? Or would it make more sense having the supply to the valve be 3/4 and then from the head and wand be 1/2? don't want to have buyers remorse since it's a one and done situation.

Or should I just replace it with new CPVC pipes? Nobody seems to really recommends CPVC pipes anymore. Also the pipes will in inaccessible when the project is done. If i missed something, please let me know.

Thanks

 

[Tuttles Revenge]

Old CPVC becomes brittle as it ages so its prone to splintering and fracturing when you're working with it. So careful cutting and care of any that you're keeping in place is critical. I like to use a fine tooth saw like a metal hacksaw blade or a Japanese saw. I prefer to transition from CPVC to other material with a solvent welded fitting when possible if you have the time to let the cement cure properly *not under pressure for 24hrs* or whatever the cement manufacture recommends.

For a single shower with 2 outlets 1/2 Expansion PEX should be fine. The porting in the shower valve is the massive reduction in flow.

I've only installed one condo project in CPVC because the original plumber who walked off the project started with it and left all the material on site. It wasn't terrible to work with, but a few dry fits that held pressure for days scared me away from ever wanting to use it again (tho propress fittings can hold pressure for years unpressed too)

 

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[TomV8]

Thank you very much for your reply. I appreciate it. The adapter I was planning on using for the CPVC is a slip weld to 1/2 expansion connector. If I went the 3/4 route, I would have to do a slip weld with a threaded male fitting connected to a female threaded receiver to 3/4 expansion.

Would you prefer using poly fittings over Sioux Chief brass fittings? I have both options the the female receiver/1/2 expansion fitting that I am planning on connection to the shower valve. I have read about class action lawsuits for some brass fittings, but I don't remember how long ago that happened. As I stated in my above post, I'm planning on using all 1/2 Sioux Chief pipe and fittings.

I discovered other PEX connections going down my rabbit hole of research, but the press and push are not readily available. Also concerned about later down the road if parts would be available. Though I could substitute.

 

[Jadnashua]

Avoid as many fittings as you can...the biggest benefit of pex is that it is flexible - the more fittings, the more restrictions. If you need a tighter bend and don't want the tension on it, use a bend support bracket instead of a 90-degree fitting when possible.

Filling the tub, using 3/4" may be better, but for showering, the 1/2" should just be barely okay with two heads. It's not as much about the pressure as the velocity, and the nozzles in the heads won't accelerate the water unless there's more water than they could otherwise flow...the restriction is what causes the water to accelerate to give you the perceived pressure you want much more than an increase in source pressure.

 

[TomV8]

Filling the tub, using 3/4" may be better, but for showering, the 1/2" should just be barely okay with two heads. It's not as much about the pressure as the velocity, and the nozzles in the heads won't accelerate the water unless there's more water than they could otherwise flow...the restriction is what causes the water to accelerate to give you the perceived pressure you want much more than an increase in source pressure.

I forgot to mention that we are going from a tub with a shower to just a walk-in shower, so no tub spout.

When you say 1/2 is barely ok, does that mean I would be better off with all 3/4 tubing and fittings? Like I mentioned before, I have no problem bumping up if there will be a perceived difference.

 

[Reach4]

would be better off with all 3/4 tubing and fittings? Like I mentioned before, i have no problem bumping up if there will be a perceived difference.

1/2 will be plenty big and will deliver hot water a little faster than 3/4 would.

 

[Tuttles Revenge]

We use plastic fittings for the most part, tho we have many brass fittings too. Mostly uponor brand but some Sioux chief too in both materials.

I think the problem was with dezincification but I think all manufactures have solved that issue by now. I've never encountered that issue with our water systems.

 

[TomV8]

I think the problem was with dezincification

yes, you are correct. Just re-looked it up and that is what it was. thanks

 

[Weekend Handyman]

I am not a plumber or a pro. I have never worked with CPVC. One thing to keep in mind with PEX is that it significantly expands and contracts in response to temperature changes. If the old CPVC is brittle, you will want to consider how the expansion of the PEX may stress the PCV and take the appropriate actions to mitigate.

 

[Jadnashua]

1/2" PEX has a smaller ID than copper. If your two heads actually can flow 2.5gpm, and you want both of them on at the same time, your available volume will be marginal, depending on the pressure available. Most heads actually are made to flow a little less than the maximum allowed to account for any slight variations and still meet code. Make sure to use the unrestricted outlet of the valve if it is one that has two outlets (tub and shower)...otherwise, your volume to the shower heads will already be restricted.

A shower head gets its outlet velocity by the incoming pressure, but mostly because the nozzles create a restriction. When the available inlet water is equal to the ability of the head to flow it without restrictions, there is NO velocity increase, it becomes essentially a rain shower head, where it dribbles out at the incoming pressure and velocity. Most people like the water coming out faster, and that takes a restriction. Take a garden hose, see how far the water flows, then put your thumb over the end, creating a restriction and see how much further it goes...it's the restriction that causes the water to accelerate, and going faster does change the pressure some, but it does change the velocity more which determines how far it can go. The more restriction you have, the more acceleration to the water jet through the nozzle, so the more volume you present it, the more output you'll get.

 

[TomV8]

I am not a plumber or a pro. I have never worked with CPVC. One thing to keep in mind with PEX is that it significantly expands and contracts in response to temperature changes. If the old CPVC is brittle, you will want to consider how the expansion of the PEX may stress the PCV and take the appropriate actions to mitigate.

The section that I would be removing/refitting is an insulated interior space and the pipe is secure/no moment, so the CPVC upstream should feel no effects unless you are thinking of something else. and if anything the PEX could help out the CPVC with any hammering that may have been occurring, but I have not heard anything like that over the years.

 

[TomV8]

1/2" pex has a smaller ID than copper. If your two heads actually can flow 2.5gpm, and you want both of them on at the same time, your available volume will be marginal, depending on the pressure available. Most heads actually are made to flow a little less than the maximum allowed to account for any slight variations and still meet code. Make sure to use the unrestricted outlet of the valve if it is one that has two outlets (tub and shower)...otherwise, your volume to the shower heads will already be restricted.

A shower head gets its outlet velocity by the incoming pressure, but mostly because the nozzles create a restriction. When the available inlet water is equal to the ability of the head to flow it without restrictions, there is NO velocity increase, it becomes essentially a rain shower head, where it dribbles out at the incoming pressure and velocity. Most people like the water coming out faster, and that takes a restriction. Take a garden hose, see how far the water flows, then put your thumb over the end, creating a restriction and see how much further it goes...it's the restriction that causes the water to accelerate, and going faster does change the pressure some, but it does change the velocity more which determines how far it can go. The more restriction you have, the more acceleration to the water jet through the nozzle, so the more volume you present it, the more output you'll get.

I don't mean to sound like I'm slow here, but I'm not 100% clear. I just want to clarify and thank you for responding. I appreciate it. First paragraph, it reads like your advocating using the 3/4 OD PEX tubing, which would be 0.677 inner D opposed to 1/2 OD with an inner of .475. I kinda interpret this as, use 3/4 PEX up to the valve and then use 1/2 to the two heads (there is no tub spout diverter). This was one of my original three plans for the setup. Also sidenote: both the shower head and the wand head also add additional air to increase pressure. To the best of my knowledge, all three outlets on the Delta Multichoice shower diverter is unrestricted and I'm only going to be utilizing three of them since the cartridge will be only have three way option.

I also interpret the second paragraph as using the 1/2 to the heads is good because it will increase the pressure/speed of the water, which is what you feel. Am I missing something?

 

[Weekend Handyman]

The section that I would be removing/refitting is an insulated interior space and the pipe is secure/no moment, so the CPVC upstream should feel no effects unless you are thinking of something else. and if anything the PEX could help out the CPVC with any hammering that may have been occurring, but I have not heard anything like that over the years.

I was thinking of the expansion / contraction due to the change in the temperature of the water in the pipe. Just something to keep in mind ... when hot water flows through the pipe it will expand quite a bit. You just need to factor that into your design (make sure you are not stressing any fittings, going to rub on anything sharp, etc). On my first few projects, ran the hot water through the pipe, before I closed up the wall, to get a sense of what was going to happen.

 

[TomV8]

I was thinking of the expansion / contraction due to the change in the temperature of the water in the pipe. Just something to keep in mind ... when hot water flows through the pipe it will expand quite a bit. You just need to factor that into your design (make sure you are not stressing any fittings, going to rub on anything sharp, etc). On my first few projects, ran the hot water through the pipe, before I closed up the wall, to get a sense of what was going to happen.

Gotcha. there should only be two gradual 90 turns for the PEX to snake from the original CPVC to the shower valve and I have 1/2 poly curves that can be mounted. I'm not going through any studs (at least not planning on it, but who knows until the floor is torn up.) since the wall that everything sits on is spaced out from the exterior. that means I have several inches between the two rows of studs.

 

[Jadnashua]

I'd run the 3/4" PEX to the valve, and 1/2" PEX would be fine to an individual head. 1/2" PEX to the valve is smaller than 1/2" copper. A typical 1/2" valve fed with 1/2" PEX may marginally pass 5gpm, the amount you might want for two simultaneous heads...that means no acceleration. That same valve, fed with copper is probably in the 6gpm range. A 3/4" valve, fed with 3/4" copper, can probably pass double that.

Every fitting you add has an accumulated effect on the dynamic pressure, and a slight decrease in the volume otherwise available.

 

[TomV8]

Thanks Jadnashua for the follow-up.

Just for fun, over the weekend, I took some time and found out the average GPM with my current shower head and tub faucet. The water lines that goes to the shower head is T'd off right before it's connected to the tub faucet which has two separate valves for H&C. I recorded how long it took to fill up a one gallon container, three times each and then averaged the time out. then divided it by 60. Here is the breakdown

• Just the shower head:
  
  • 2.57 gpm (to be expected for flow restrictions for shower heads. i may try and do this again without the shower head. I'm curious about how much flow gets reduced from the four 90 degree fittings in the cold line leading to the valve and from the valve itself.)
• Shower with tub faucet with both H&C valves full open:
  • 1.65 gpm
• Shower with tub faucet with just C valve full open:
  • 1.986 gpm (previously in the shower I did turn on the tub faucet with both valves open at what you would probably typically would, I did notice a drop in flow, but it wasn't really that bad. acceptable. Though the tub flow was pretty crazy.)
• Just tub faucet with both H&C full open:
  • 10.0 gpm (my opinion of the flow was really a lot.
• Just tub only with only C valve full open:
  • 6.295 gpm (also seemed like a lot)

 

[Jadnashua]

FWIW, when doing remodeling, you're required to update the valve to one that meets the safety, anti-scald requirements, and those tend to not flow as much as an older one with separate hot/cold faucets...

At 60psi, a shower head cannot flow more than 2.5gpm, and legally be sold in the USA.

 

[TomV8]

FWIW, when doing remodeling, you're required to update the valve to one that meets the safety, anti-scald requirements, and those tend to not flow as much as an older one with separate hot/cold faucets...

At 60psi, a shower head cannot flow more than 2.5gpm, and legally be sold in the USA.

Thanks. I'm going to install this model with stops, or at least super close to this model and the roman bath faucet is being donated since we are going from a tub w/ a faucet and a shower valve to a walk-in shower with just a shower valve. So anti-scald is included due to the one handle design.

This may be my final amateurish question. Since I'm going the 1/2 CPVC to 3/4 PEX A route, my two options seem to be the following since I cannot find a 1/2 CPVC to a 3/4 PEX A adapter anywhere.

• A. 1/2 CPVC slip-on weld male brass threaded adapter screwed with plumber tape and dope into a 1/2 female brass threaded receiver 3/4 PEX A barb
• B. 1/2 to 3/4 CPVC Reducer (though in this case it's reversed) > 3/4 CPVC pipe for a few inches connected to a slip-on weld 3/4 CPVC to 3/4 PEX A adapter fitting

Thoughts one which option I should go with or is there another? My thinking is to go with option A.

 

[John Gayewski]

Glue a bushing into this fella

 

[TomV8]

Glue a bushing into this fella

Would you have a link to for the product because I haven't seen any 1/2 cpvc to 3/4 PEX expansion. Even Uponor doesn't have one.