Copper To PEX New Basement Shower - Advice?

[Zerocool749]

Hi everyone,

I'm adding a three piece bathroom to my basement and I'm planning how to branch off my existing copper supply to feed my new bathroom shower, toilet, and sink. Luckily, I have the hot and cold for my upstairs bathroom located right near where I am adding this bathroom in the basement. So my plan will be to T off of that. This will be my first time using PEX.

Here is my diagram of how I'm going to do it.

My plan is to run the PEX through the floor joists to where I will make the T connection for the shower. I'll add shutoff valves that will be accessible from the exposed ceiling in the closet next to this bathroom. Then I will run the PEX inside the joist cavity to the wall for the toilet and sink. Then down the wall cavity for the toilet and shower. I plan on drywalling only the ceiling in the bathroom and not the other rooms in the basement.

Other questions:
1. What size PEX do I use? 1/2"?
2. Should I use copper for all of the crimp rings, elbows, tee connections, and stub outs?
3. Is PEX-B fine? That's what Menards sells from Sioux Chief, their PowerPEX brand.
4. Do you have any other advice for this job? Any feedback on my plan?

Thanks for your help! You guys are awesome and I try to pay it forward for other people in my profession.

 

[Jadnashua]

First question is what size line is feeding the existing bathroom? If it's 1/2" copper, you probably won't like how things work when you try to feed a second bathroom with it!

If it is 1/2", you might try running 3/4" pex and then splitting that into two branches of 1/2" with one feeding the shower, and the second one the sink and toilet.

On any copper line per the Copper Institute's guidelines says the flow on hot should never exceed 5fps. On a 1/2" copper pipe, that's only 4gpm. An industry standard shower head is limited to NGT 2.5gpm, so running both would be pushing the limit, especially in the winter when you'd need mostly hot since the cold is so cold. In comparison, a 3/4" copper pipe at 5fps can supply twice as much at 8gpm, and is fine. If the new bath has a tub, that extra gpm will be noticeable if both bathrooms are being run, or if one of the showers has more than one showerhead.

Note, depending on where you live, your state might have a more restrictive showerhead gpm than the national 2.5gpm run. A tub by itself can pull more than 4gpm of hot, so if that was happening while someone else was using some hot, it would degrade performance.

 

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[Zerocool749]

The outside diameter of the copper hot and cold lines feeding the existing bathroom are 7/8", so I think it's a copper pipe size of 3/4" Based on what you said, I should be fine?

Also, the issue you're describing is when both showers are running at the same time, right? That could happen, yes. Also, the new bathroom does not have a bathtub, it will only have a shower.

Thanks for your time in reviewing this!