Shower Leak, pipe questions and future planning

[Jadnashua]

Download this document https://www.copper.org/publications/pub_list/pdf/copper_tube_handbook.pdf it will tell you more than you want to know about volume, pressure losses, maximum recommended flow rates, etc. If you go with pex, keep in mind that the fittings create more frictional losses than copper because the fit INTO the pipe, rather than around it like copper fittings, but the advantage is that you can probably minimize how many you need. For short distances, a pex fitting can act like a venturi, causing the water to speed up while going through the restriction (sort of like your finger over the end of a hose) and then slow back down again, without losing too much in pressure. If installed like copper, with elbows rather than just bending the pipe, you lose a lot of the advantages, add a lot of cost, and will create LOTS more frictional losses and volume issues.

A typical shower head sold can't flow more than 2.2gpm. A tub valve can flow 6-8gpm. The max recommended flow rate of 1/2" copper is in the order of 4gpm, but it will support more, depending on your pressure and you're getting supplied by both the hot and cold lines. Filling the tub while trying to take a shower is the issue if both are trying to pull from the SAME 1/2" pipe. If you branch off the 3/4" line with TWO 1/2" runs, you should maximize your performance with what you have coming in.

 

[Chris Wagner]

Would the advantage of branching 2 separate 1/2" PEX lines to each shower be because then there would be less fittings? Because they would still be pulling from the same 3/4" line that runs to the bathroom if they are branched separate or just T off like it currently is. Thats the only thing I can see why it would be different?

 

[Sponsor]

 

[Jadnashua]

Area of 3/4" = 0.375^2*3.14 = 0.44sqin opening. Area of 1/2" = .25^2*3.14=0.2sqin. By reducing the feed to BOTH your tub/shower and shower, you're trying to feed them both with that smaller volume - say they each were flowing, you'd have 0.1sqin if the flow was split evenly between the two and if you're trying to fill the tub, that won't happen. But, if you immediately branch the 3/4" line into TWO 1/2" lines, you'll have essentially NO restriction on each 1/2" line and have the equivalent of that full diameter 1/2" pipe full of water feeding EACH room.

The water will try to speed up a little when you've run it into a smaller pipe, but that's not good for either noise or long-term life of the pipe. That document I linked you to discusses flow velocity, and you should not design something that forces the flow to be higher than the 5fps on the hot line.

If it were just two showers, you may not notice. But, as soon as you're trying to fill the tub on one while trying to take a shower in the other...you'll notice, and the fix is easy now...not later.

 

[Chris Wagner]

I took a look at the document but was wondering if numbers would be off since I'm talking about doing this with PEX. But I think I'm understanding more now. Was this originally plumbed wrong? Or its just better to do it this way now?

If going that route would I use This Adapter? One of those would needed to be sweat on to each 3/4" copper line. Then a small piece of PEX then a Tee splitting each line from there? I cant seem to find any sort of sweat on Tee

 

[Cacher_Chick]

If you are going to use 1/2" PEX for each fixture, each 1/2" line should come off the respective 3/4" line.

1/2" PEX has a smaller I.D. than 1/2" copper, and neither is adequate for supplying both fixtures in a back-to-back tub/shower installation unless you don't mind the reduced volume when both are placed into use.

 

[Jadnashua]

I took a look at the document but was wondering if numbers would be off since Im talking about doing this with PEX. But I think Im understanding more now. Was this originally plumbed wrong? Or its just better to do it this way now?

If going that route would I use This Adapter? One of those would needed to be sweat on to each 3/4" copper line. Then a small piece of PEX then a Tee splitting each line from there? I cant seem to find any sort of sweat on Tee

I'd put a 3/4" copper T on your 3/4" supply, and then convert the two outlets to your 1/2" pex. Or, for maximum volume to the tub/shower, you could run 3/4" pex to it, and make the connection to the valve after converting it to 1/2". You could do the same to the master shower, but it wouldn't need it. It could benefit should you decide you wanted to run more than one showerhead in the master shower, though.

While I haven't looked for it, there's probably a similar document for pex as the copper tubing one I linked you to. There are differences in the type of pex and fittings, too. Something like Uphonor that uses an expansion tool has a larger ID through the fitting than one that uses crimp rings. On that type of pex system, the fitting must be smaller so you can slide it into the tubing, then the crimp holds it in place. On the expansion system, the fitting is larger in both ID and OD, and to get it into the tubing, you use the tool to literally stretch the pex out, slide the fitting in, then the memory of the plastic tubing collapses around the fitting, making the seal and holding it in place. As a result, it can flow (slightly more). Keep in mind that the area of the opening changes as a square of the radius...a small difference becomes a much bigger one than the size would otherwise imply. That's why a 3/4" pipe has over twice the flow volume of a 1/2" one while only being 50% bigger, the volume it can carry is over 100% more.

IOW, you want to keep the pipe size as big as your supply until you can split it into smaller sizes that can meet your individual needs. DO NOT take the 3/4" copper, neck it down to 1/2" later convert to 1/2" pex...go from the 3/4" copper to two 3/4" outlets in a T, THEN convert it to the 1/2" pex or copper (or keep it at 3/4" pex until it needs to be 1/2").

The OD of pex is fixed across the brands...the ID can vary some (it's not much), which is why the manufacturers say to use their fittings for best results.

 

[Chris Wagner]

Yes I read the Uponor Manual but it doesnt dicuss flow rate,etc. Im still deciding between Uponor or Viega, I was leaning Uponor but
I actually spoke to the local rep for Viega in my area today. He directed me to a local supply house that stocks all the fittings, so that's very convenient. Even offered to stop by the house if I needed.
But I asked him his advice on the subject, he was a licensed plumber in area for 27 years. He said convert the 3/4" copper line to PEX then run 3/4" PEX to the kids shower/tub then use a 3/4 x 1/2 x 1/2 Tee and connect both Valves from there. Either way he said would work,,

 

[Jadnashua]

Because a 3/4" line has a bit over twice the flow of a 1/2" line, yes, you'd then have decent flow done that way. You'd have more if you converted the copper in 3/4" to two 3/4" copper outlets, then dropped it, but the difference may not be all that much. If you kept the 3/4" pex from both outlets all the way to each valve, then dropped it to 1/2" (assuming you're using 1/2" valves), you'd always have the max the devices could use. What you do not want to do is drop it to 1/2", and then split it into two more 1/2". You will be disappointed in the master shower if someone is also filling the tub, and the tub will take much longer to fill as well. Ratio of area 0.75:0.50 is
0.141:.06 or about 2.25:1 achieved by squaring the radius of 0.75 pipe verses 0.50 pipe. Now, copper isn't actually exactly that size ID, but pex is smaller, so the ratio will vary slightly.

Smaller pipe has more friction, so as you approach maximum flow rates, you'd lose more pressure which is why you might just try to keep it 3/4" all the way, then drop it to fit the valve. Disadvantage to that is that there will be more cold water in the line to purge when first starting up. This is where a hot water recirculation system can make things nice. Before I installed one, it would take over a minute to get hot water to my shower in the morning...after, about 5-seconds.

 

[41Fever]

If you are thinking of replacing the Moentrol valves, be sure to orientate your hot and cold piping on each valve as many new pressure balancing valves don't give you the option of "rotating" the stem to correct the current piping setup.

 

[Chris Wagner]

Hello again, Quick recap: There was alot of discussion on piping size to a back to back shower.

Ended up bringing both the 3/4" copper and transition to PEX over more towards the valves. Its had water pressure for about 2 weeks now with no leaks in solder joint or PEX. Please attached photo and see if everything look ok?

I ran the following test. All times are filling a 5 gallon bucket
New tub fill 1:08
New tub fill with 2nd bathroom shower running 1:12
New shower only(2.5 head) 2:41
New shower with 2nd shower running 2:49

Thoughts? I can make adjustments now if necessary

 

[Jadnashua]

Not much variation. You might notice slightly different times in the winter when your incoming cold is more frigid...you'll be using less cold water, and more hot in the relative proportions. 1" pex has close to the same ID as 3/4" copper, and may have made a slight difference.

 

[hj]

One thing you mentioned earlier was that you wanted to use PEX so you could extend the hot and cold to other items> Those items, a handheld, etc. do NOT get hot and cold water to them. They are connected to the tub and shower valves so they do NOT affect the hot and cold pipes to the valves.

 

[Chris Wagner]

Hi Hj,
I might have described wrong. I meant the reason for using PEX was when the master shower gets redone possibly more stuff(handheld,rainshower,etc) would be added. With both showers sharing this wall my theory would it would be easier to route the PEX for these things FROM the valves. You can see here I hooked up the handheld from the valve and tub spout is all copper. The other valve is connected from the Tee's with sharkbites since that bathroom will be redone next.

 

[Chris Wagner]

Even though showerhead is 2.5gpm seems I'm getting more like 1.85. Is this just due to distance(2nd floor)?

 

[Jadnashua]

The gpm ratings are at a specified pressure...if your pressure is lower, your output will be lower, too, and conversely, if your pressure is above where it was rated, the gpm would rise. Would need to know your static pressure. Water pressure drops at about 0.43#/foot of elevation change, so measuring it in say the basement verses the second floor should result in different values.

 

[Chris Wagner]

Took showerhead off and just used hose to test both shower risers . The tub/shower bathroom got 3.1 gpm and shower alone(master) got 3.75gpm.

Basement shower with same hose was 5.1gpm