PEX-A sizing help needed

[Nitrousbird]

Situation: Doing a partial basement finish/remodel. House built in 2004 and basement was partly finished during that time. Bank owned home; the previous owner basically ripped out the partly finished basement due to sump pump backup (they took the insurance money).

I am refinishing the basement and upgrading - I'm nearly finished. Upgraded the 1/2 bath to a full bath. All plumbing connections are in the unfinished side and easily accessible. The facts:

- Feed to the 1/2 bath is 1/2" copper. It is fed from a T-split, that is 3/4" in, 3/4" out on one side (that feeds the master bath that's pretty far away) and the 1/2" to the bathroom.
- The bathroom is very close to the supply lines. Probably 10' of line from the hot water heater to the bathroom. Maybe 20' total from where the water supply hits the house to the bathroom
- The shower is a multi-function setup, including 3 body sprayers, rain shower head and bar mounted handheld setup - all Delta gear
- 3/4" NPT female in, 1/2" female out drop ear fittings for the shower head and handheld
- 6-way diverter/shower control combo and body sprayers are male 1/2" NPT. Basically, if Delta made it, it's 1/2" NPT

I am going with Pex A because I believe it is the superior connection between all of the PEX option, the best bend tolerance and doesn't lose flow at the connection point (a major consideration for sizing as I understand it). I realize the parts are a bit pricer and harder to obtain; I'm doing PEX-A, already bought the prep tool - it's a done deal.

My questions:
#1: Do I need to change out my feed to the bathroom to 3/4" copper from the current 1/2"? Taking into account this is a basement shower (so no lift loss) and short runs. I have not measured my water pressure but it is decent throughout the house. The toilet/sink would never run the same time as the shower in this bathroom (it isn't big enough to be a 2-person deal), so no reason to take that into consideration.

#2: There is no such thing as a 1/2" Female NPT to 3/4" PEX-A fitting. Can't be found. There is 1/2" copper sweat to 3/4" PEX-A, but my copper skills aren't great (one of the reasons I'm going PEX), so I am doing my best to minimize what I have to sweat in. Because of this, am I safe to run 1/2" PEX A to all of my connections (assuming the answer to #1 is needing 3/4" copper, otherwise 1/2" PEX-A would make total sense).

I guess my thinking is that if the inputs to my shower fixtures are all 1/2" NPT, what purpose would upgrading to 3/4" serve in this application? Obviously, if it was a 2nd story bathroom or a long run it would make sense; but I'm having trouble understanding how 3/4" would help me here even though my general research has indicated 3/4" should be used for full baths.

 

[Jadnashua]

1/2" supply line can run ONE shower head really well, and MAYBE two, but you will notice a significant difference if you try to run three at the same time.

As long as nobody on that 1/2" line would be flushing a toilet or using the sink, what is going to the shower will only have the above limitations.

FWIW, on a copper line, the industry standard recommendation is to not exceed 5fps flow rate with the hot water. On that 3/4" line, that equals 8gpm. You'll be mixing some cold in normally, but if the valve is 1/2", with its internal orifices, they rarely can flow more than about 6gpm. On a 1/2" copper line, at 5fps, that's only 4gpm. Depending on how hot your hot water is set and how cold your cold supply is, I think you may see part of the issue. The ID of pex is smaller, but they allow it to flow faster, coming close to the same values as with copper.

You can also look at it this way...on that 3/4" main line, if you adhere to the 5fps velocity limit, and you're getting 4gpm to the shower on the 1/2" line, you only have 4gpm on the hot line to feed your master bath before you exceed the industry guidelines. Pushing more through causes noise, lowered pressure due to friction (static pressure would be the same), and potentially, eroding the inside of the pipe itself.

 

[Sponsor]

 

[Nitrousbird]

1/2" supply line can run ONE shower head really well, and MAYBE two, but you will notice a significant difference if you try to run three at the same time.

As long as nobody on that 1/2" line would be flushing a toilet or using the sink, what is going to the shower will only have the above limitations.

FWIW, on a copper line, the industry standard recommendation is to not exceed 5fps flow rate with the hot water. On that 3/4" line, that equals 8gpm. You'll be mixing some cold in normally, but if the valve is 1/2", with its internal orifices, they rarely can flow more than about 6gpm. On a 1/2" copper line, at 5fps, that's only 4gpm. Depending on how hot your hot water is set and how cold your cold supply is, I think you may see part of the issue. The ID of pex is smaller, but they allow it to flow faster, coming close to the same values as with copper.

You can also look at it this way...on that 3/4" main line, if you adhere to the 5fps velocity limit, and you're getting 4gpm to the shower on the 1/2" line, you only have 4gpm on the hot line to feed your master bath before you exceed the industry guidelines. Pushing more through causes noise, lowered pressure due to friction (static pressure would be the same), and potentially, eroding the inside of the pipe itself.

The results are in. I went with the 1/2" everything. My Delta 6 way diverter only does two items at a time. Even with my 16" rainshower head (which is almost too big) and 3 body sprayers, the water pressure is great.

My hand held's pressure is crap, even on its own, but that has to be a separate issue I need to work out as there is no way 3 body sprayers have tons of pressure yet it has nothing.

With the PEX-A, there isn't a size loss to cause a drop like other PEX setups. I found it pretty easy to work with as well. Overall, I am glad I went this route.