PEX to tub spout- How much will it impact flow rate?

[Bird Doo Head]

I am plumbing in a new Grohe tub-shower faucet that conencts to Rapido Smart Box. It is supplied by 1/2" NPT hubs. There are 3 total outlets: Overhead shower, hand shower and tub spout. The tub spout won't be used when the shower(s) are on.

To pipe the tub spout with copper will be quite a challenge due to framing to reach around during torch work.

I can rather easily plumb with 1/2" PEX and expansion ring fittings.
The run will have (1) male adapter, (3) 90-degree turns & (1) PEX x Sweat straight fitting. One of the 90 turns has to be a PEX expansion ring elbow. The other can be a bend support and the last can be a copper drop-ear 90 or bend support turn.

Unfortunately, the inside diameter of PEX fittings is just about 3/8". There isn't room to increase to 3/4" and
reduce back down.

I have read dozens of flow rate and pressure drop charts and articles. None agree. Does the reduction by using PEX versus copper have a great impact on the time it takes to fill a bathtub?

Thanks for sharing your exerience & knowledge. It's appreciated.
Paul

 

[breplum]

1/2" PEX can be an issue feeding a tubspout. Quite a few mfr's instructions where a diverter tub spout is involved say to NOT use 1/2" pex in those cases.
Depending upon which internal valve assembly you are planning to use, read those specific instructions to check any stated prohibitions.
Does the reduction by using PEX versus copper have a great impact on the time it takes to fill a bathtub? Yes, some impact.

 

[Bird Doo Head]

Thank You Breplumb for taking time to reply & for your suggestions.
Interestingly, this valve has 100% shut off for each device, so there wouldn't be any water from the shower head when the tub is filling. (I always thought 100% shut off for a shower head was kind of dangerous, but it seems it is not prohibited)

Thanks for your mention of the impact of PEX on tub filling time. After reading it, I think it may be worth the effort to move the framing as necessary to plumb with copper.

Thank You Again,
Paul

 

[TomFOhio]

Plus the tub spout could be floppy since its not ridig. Copper is the best way to go

 

[Bird Doo Head]

Thanks TomFOhio for your note about PEX and the spout.

I was able to re-work some framing to plumb the tub all copper. The shower head, however, brought its own challenge. So I thought about PEX for it.

Experiment:
For fun today, I connected a short length of PEX-A (expansion) to a PEX x NPT fitting and to the 1/2" fed Chicago Faucet shop sink. I measured 7.5 gallons per minute. (Being the bird doo head than I can be, I forgot to write down the pressure.)
Faucet alone was 12.8 gpm.

So, it seems that PEX will be sufficient for the 2.5 gpm shower head. The drop-ear & a straight length will be copper, but I'll use 10" of PEX for a 3/8" offset between the copper and the Grohe Rapido box. The other two outlets (hand held shower and tub spout) and the supplies will be all copper. The Rapido box is 1/2" NPT on all. It will be supplied with copper for inlets.

Thanks Again Guys for helping. I learned a lot here.
Paul

Unrelated But Maybe Handy To Someone Someday-
My Insurance Pads for torch work close to combustibles are out on loan, so I bench tested 1/2" Durock cement board with about 4 minutes of ox-acetylene (overkill) in a 2 inch circular motion. It worked great, despite the mesh holding the board together. I suppose MAPP would be even a lower temperature rise.

The thermocouple between the board and the stainless table was 5.2 degrees-F above the table surface 18" away from the action. So saving cement board scraps may come in handy some day. Can't bend them around stuff like Insurance Pads, or tack thm up with push pins, but cement board scraps are good for a straight shot. Hopefully this side note will come in handy for someone someday.

 

[Bird Doo Head]

I hate to be a bother, but one more question arose (so far) on my faucet plumbing project. The Grohe Grotherm Smart Control Valve closes very quickly, so there is some water hammer. Unfortunately, I had asked Grohe if they were needed & was told no, the valves close slowly.

Installing an old-school air chamber or even a mini pre-charged unit near the valve will probably be impossible because of pocket door framing on the opposite side of the wall. There is no space to run tubing up above the valve or horizontally next to it.

My idea was to install pre-made piston type arrestors on the supply lines in the basement. (One on each hot and cold).

A drawing is attached with two choices. Location A will be about 40 pipe inches from the valve and location B will be about 62" away. (All 1/2" Type L copper tubing)

I am wondering if these will help when they are rater far from the valve.
Thanks for sharing your experience & advice.
Paul