Sizing PEX for Shower

[Rich45]

My apologies in advance if this has been asked and answered in another forum or thread.

I am in the middle of a bathtub to shower conversion; as part of this remodel, we had to pull up the subfloor (rotted) and re-locate water lines because they came up through the subfloor where the shower pan should go.

The entire upstairs is fed by a main 3/4" copper line (1 for hot, 1 for cold), with feeders to each fixture using 1/2" copper pipe.

The contractor doing the work wants to do PEX from the 3/4" copper line to the shower, and use 1/2" PEX. The run is relatively short, maybe 10 feet.

Since we're redoing this anyway, should we stick with 1/2" PEX or upgrade to 3/4"? The shower had flow issues before, but I think it's because the cold line was kinked when bending to come up through the floor and the hot line has a dent in the tee. Everything else upstairs (toilets, sinks, washer connection) is 1/2" copper. I'm insisting if he uses PEX, he uses the expansion fittings and PEX-A.

Thanks for your insight!

 

[John Gayewski]

Water pipe sizing doesnt come intuitively without taking some measurements. No one here can answer you without knowing specifics.

If the contractor (i hope your talking about a plumbing contractor and not a gc) will have to show you that the shower functions as designed after its done. If he cant then its improperly installed and you shouldn't pay until it is. Very important to withhold payment until you have proper performance.

 

[Sponsor]

 

[wwhitney]

How many shower heads with what flow rate(s), what shower valve? For a single 2.0 gpm shower head, 1/2" PEX is better for the hot, less water to waste, less time to wait. For (3) 2.5 gpm shower heads, 1/2" PEX is likely too small.

Cheers, Wayne

 

[Rich45]

Thank you guys for the response!

Wayne, the flow rate is no more than 3.5GPM, I will have a max of 2 shower heads - 1 on the wall and one handheld.

John, the contractor is probably not a plumber - he does tile and bathroom remodels. I got the sense I knew more about PEX than he did - not good. Maybe I should get a plumber involved, but I was hoping to keep cost down.

Yes, I know - it's going to cost me more not to.

-Rich

 

[wwhitney]

Here's a calculation that may inform your choice:

If we say that the 1/2" hot PEX (ID = 0.475") is going to be carrying 3 gpm (some cold gets mixed in), and that it's 20' of effective length (includes the equivalent length of the fittings on the end of the 10' of PEX pipe), then the pressure drop on that segment will be 2.4 psi.

http://irrigation.wsu.edu/Content/Calculators/General/Pipeline-Pressure-Loss.php

Cheers, Wayne

 

[Jadnashua]

1/2" pex is fine for one shower head, and might be okay for two as long as they aren't both the 2.5gpm max allowed. FOr best performance, pex should be installed with the minimum number of fittings...i.e., if there's room, bend it rather than putting in a fitting to turn it. If you need a sharper bend, up to the max allowed without kinking, use a bend support that snaps around the pex to create the 90-degree bend. Each fitting adds resistance/friction, and will lower your dynamic pressure and lower the maximum volume available.