PEX Question on Remodel

[alex rodriguez]

Question: Am I better off going through the trouble of finding 3/8 PEX fittings? Or should I use an adapter and change the 3ft of pipes closest to the shower to 1/2 and use the standard 1/2 fittings I can find almost anywhere ??

Background!!:
So I recently bought a house in Georgia that uses a PEX manifold system for all the plumbing in the house. They have 3/8 PEX pipes for everything including the upstairs tub, sink, and unfinished shower. I haven’t noticed any problems with water pressure in the downstairs kitchen or bathrooms. Upstairs no problem either, only thing is the tub is a little slow to fill but I’m ok.

The upstairs shower was left unfinished and I’m starting to tackle that and install a stand-alone shower head. There are the hot and cold supply PEX pipes sticking out of the wall waiting for me, both 3/8. I’m having trouble finding 3/8 fittings and have been reading that 1/2 or even 3/4 would be much better to have had, but I’m working with what I got. So my question is am I better off going through the trouble of finding 3/8 fittings? Or should I use an adapter and change the 3ft of pipes closest to the shower to 1/2 and use the standard 1/2 fittings I can find almost anywhere ??

I don’t have a lot of wall I can open up so that’s why I’m not considering changing the whole line to 1/2, just near the shower fixture. I’m worried with it being upstairs that the opening to a larger pipe will cause even worse water pressure issues. Any suggestions?!

 

[WorthFlorida]

For just 3 feet you should be OK.

https://codes.iccsafe.org/content/IPC2018/appendix-e-sizing-of-water-piping-system

 

[Sponsor]

 

[Reach4]

1/2 inch will not cause a loss of water pressure. The biggest advantage to 3/8 is that it lets the hot water arrive sooner. Most people don't use 3/8 for the reasons that you noted-- it costs more and is harder to get. Also it lets you use fewer sizes to use 1/2 for situations even where 3/8 might have an advantage.

However I would not think 3/8 would be good for a tub, because it will slow down the filling vs 1/2.

 

[alex rodriguez]

1/2 inch will not cause a loss of water pressure. The biggest advantage to 3/8 is that it lets the hot water arrive sooner. Most people don't use 3/8 for the reasons that you noted-- it costs more and is harder to get. Also it lets you use fewer sizes to use 1/2 for situations even where 3/8 might have an advantage.

However I would not think 3/8 would be good for a tub, because it will slow down the filling vs 1/2.

I’m leaving the rest of the plumbing, but would it cause any issues for me to adapt the 3/8 supply to 1/2 right before the shower valve? Here in the picture I would adapt to 1/2 and then connect the shower valve, head, etc

 

[Terry]

You don't really have a choice. The tub valve is 1/2" and the incoming is 3/8".
Bumping up to 1/2" will be fine.

 

[WorthFlorida]

Looks like you have enough slack to reach a shower valve body that will allow a direct connect to it. If you can find a 90 degree shark bite with 3/8 press fitting and 1/2 thread would be the way to go or 1/2 elbow then one of these couplings.

https://www.supplyhouse.com/SharkBi...ZvDmn8NRv7wQfSpnpL1evw7UJpwIhX4MaAhm8EALw_wcB

 

[Jadnashua]

FLow restricted items should work fine with 3/8", but anything that isn't flow restricted already will be if you use that size piping. If you've got long runs, I'd prefer to use a hot water recirculation system to minimize the arrival of hot versus still having to flush the line and throw it away, regardless of the size of the tubing. There's a maximum velocity specified for most types of water supply piping. The actual timing, assuming the outlet can handle the volume, would be the same with 3/8" or 1/2" (or even larger if the valve isn't restricted)...you'd just be wasting more water to flush out the cold before the hot arrives.

https://www.pexuniverse.com/pex-tubing-technical-specs The volume in 1/2" pex versus 3/8" is 184% more at the same velocity. So, as you've seen, filling the tub is slower...the piping can't handle the increased demand. Personally, I would never run 3/8" to a tub/shower or washing machine or hose bib. ALl of those things work better with a higher capacity supply line.