PEX 90 fittings how much impede water flow?

[Scouper]

I am a homeowner and recently have had PEX installed in a bathroom renovation. They put a lot of 90° fittings in to work around the joists and up into a shower area. I thought the idea with PEX was to reduce the number of fittings it seemed like there were fittings that could have been avoided. Is it best practice to do 90s to keep things neat or snake things around to keep the runs with l fittings? The plumber said the shower flow valve reduces the pressure anyways so it really didn't matter even if there was a little bit of reduction. Anyone have any thoughts in this area? My photograph shows the work that was done I circled where the elbow joints are and in red I drew where I thought you could have snaked the PEX without so many fittings

 

[John Gayewski]

As a sloppy rule every 90 adds 10ft of pipe.


You're homes incoming pressure and elevation above the meter are the two factors that make the most difference in shower volume.

Some plumbers believe that bending PEX will eventually cause it to leak (like it did with previous versions of plastic pipe for domestic water).

Is your new shower valve installed yet?

 

[Sponsor]

 

[Scouper]

As a sloppy rule every 90 adds 10ft of pipe.


You're homes incoming pressure and elevation above the meter are the two factors that make the most difference in shower volume.

Some plumbers believe that bending PEX will eventually cause it to leak (like it did with previous versions of plastic pipe for domestic water).

Is your new shower valve installed yet?

Yes in fact it was this that made me start thinking about all the 90ss because I asked him to move the valve over a bit because we hadn't accounted for the new Left wall of the shower so by moving it over he had to cut out that stud and then redo the water and it seemed a lot to put another 2 fittings in.

 

[Jeff H Young]

2 90s on the cold and 4 on the hot? with no other situations suggesting that piping was a real long run or undersized, I wouldn't expect a problem on a shower

 

[Jadnashua]

A fitting adds to the effective length of a pipe run. This is true on any type of tubing, but the values will differ based on the individual properties of the pipe/fitting involved. You can get a very accurate estimate of the effect of adding fittings to the run by looking at the design manual for the brand of tubing and fittings you're using that is usually available for free on the company's website. It will say something like 'a 90-degree bend adds 4' to the effective length of the run'. Then, you go to the table that has the total effective run at the volume used, to get the pressure drop. So, yes, every fitting added will drop the dynamic pressure, and that will decrease the available volume, but it probably won't make that much difference unless you're already at the design limits of the things you want to accomplish. IMHO, one of the major advantages of pex is the ability to avoid almost all fittings. This maximizes the flow, minimizes the dynamic pressure losses, and makes for fewer potential leak points and less costs and time to install. In most cases, if you need a sharper bend, a bend support is cheaper than the fitting, plus it is quicker, so less labor, too.

 

[Tuttles Revenge]

You're likely installing a shower head that max's out at 1.8gpm, but more likely its 1.5-7gpm... The water being supplied even through all those elbows greatly exceeds what the shower head can handle... even if you put in an old 2.5gpm head.

I personally use bend supports in any place I can vs elbows, but its not a hard and fast rule.

 

[Jadnashua]

Minimizing the dynamic pressure losses becomes critical when you're planning a high volume like trying to fill a big soaker tub as quickly as possible, or you have a human car wash situation with lots of shower heads. There, you do not want to induce any unnecessary restrictions and lots of volume capacity...otherwise, it's no big deal. A showerhead only provides the design capabilities when the supply can produce more volume than the restriction (nozzles) in the shower head can pass...this causes the water to try to maintain the volume, and to do that, it speeds up through the restriction. If it can easily pass all of the volume available, there's nothing to try to make it go faster, sort of what you get with a rain shower head...lots of outlets, no acceleration, so it sort of just dribbles out.

 

[Jeff H Young]

Less fittings is best. Hands down. Not much reason to prefer a bunch of joints and restrictions

 

[vandi]

Wanted to come here to say thinaks for the info. A "plumber" had installed a whole house filter and softener and added 7 90s and 2 splices on 3/4" pex-b (main in is 3/4" copper). Any time I flushed the flow to any taps that were turned on went to 20% or so (40 psi drop). I replaced the giant zig zag of 90s and all of the pex B with a straight (nice wide sweeping turns) run of 3/4" PEX-A... VOILA problem solved. This is the thread that the google algorithm brings up at the top of the list when you google "90 degree pex flow restriction" so I thought it prudent to resurrect the thread and provide the feedback. Thanks for the forum and all of the great information here.