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I was advised to use 1/2 PEX for the hot water and 3/4 Pex for the cold water The bathroom has shower, sink and toilet Do I need to reduce to 1/2 when I am branching to the fixture ? I can't find ball quarter turn shutoff angle valves that go from 3/4in PEX to 5/8s

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  • So for the cold line you are coming into the bathroom with 3/4" PEX and then branching to lavatory, toilet, and shower? I would say going to 1/2" PEX at that point for lavatory and toilet would be right (nothing larger needed). What size pipe does your shower valve take? Normally AFIK there is not a separate cut off valve for the shower. Some shower arrangements require high flow and so a 3/4" cold line all the way to the shower valve might be future proofing even if you don't need it now. Personally I use a low flow head and consider a rain head and side jets an outrage, but some want that. Apr 21 at 2:00
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"Need" is defined by the connection you want to make. As you've discovered, shutoff valves (supply stop valves for use with a fixture) with 3/4" inlet practically don't exist. Therefore yes you'll need to adapt the plumbing to the inlet of whatever shutoff valves you can find. Shutoff valves are widely available with inlets of either 1/2" female iron pipe thread or 1/2" nominal compression (the latter is called 5/8" tube size by some). With those two sizes as your destination, it's time for another visit to the "which fittings are readily available" department.

A copper stub-out is a common choice. It crimps to the in-wall PEX tubing and stubs a section of copper pipe/tubing through the drywall. After the room finish is completed the capped end of the pipe is cut off and a compression inlet shutoff valve is installed. You'll have a hard time finding a 1/2" stub-out that fits 3/4" PEX, though, so that indicates you'll next have to hunt for something like a 3/4"x1/2" PEX reducing tee, elbow, or coupler.

Another possibility is to arrange to emerge from the wall with PEX tubing directly. In this case you might get a 3/4" PEX x 1/2" male pipe thread adapter and pair it with a 1/2" FIP inlet shutoff valve.

There are few rigid requirements in the practice of plumbing -- mostly it consists of following a few principles and getting the job done with whatever parts are readily available.

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  • I install 3/4" shutoff valves ALL THE TIME. Where are you at where these are unicorns?
    – DMoore
    Apr 21 at 7:05
  • @DMoore I think the unicorn is OP's description of a valve that serves as a reducer per "I can't find ball quarter turn shutoff angle valves that go from 3/4in PEX to 5/8s". I would guess that Greg omitted the 5/8s and is referencing OP's unicorn.
    – MonkeyZeus
    Apr 21 at 12:22
  • I shop on Amazon.ca so if it is there I will get it. @Greg Hill: yes that is my plan, come out of the wall with PEX. I am trying to avoid soldering and use as few fittings in the wall as possible. If there is an option to transition at the end of the pipe from 3/4" to 1/2" and install a shutoff valve there, I will go with that i.imgur.com/Xz4Fnvl.png -this is the way I want to do it
    – MiniMe
    Apr 21 at 14:00
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    @DMoore MiniMe referenced sink and toilet fixtures and I thought of supply stop valves. I don't recall ever seeing such a valve with a 3/4" inlet and none is available at my local Home Depot nor Lowe's either. Their stock is primarily 1/2" FIP and compression with a smattering of 3/8, PEX barb, and sharkbite. Ordinary isolating valves, hose bibbs, etc -- sure, those are available in 3/4" anywhere.
    – Greg Hill
    Apr 21 at 16:12
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You can keep it all 3/4 PEX, or you can reduce it to 1/2 to save money and space, or to deal with parts availability.

Most fixtures (sink, toilet, tub, shower) don't need 3/4 all the way, but it is not forbidden or bad to do so.

When branching off, you can use a PEX Tee fitting that also reduces. You can branch off at 1/2 at each fixture, and continue with 3/4 until the next branch off. Then for the last branch off you can get a "3/4 to 1/2 and 1/2" Tee.

Here's a Tee for a 1/2" branch-off that continues 3/4. You can use this if a longer stretch follows before several more fixtures:

enter image description here

And here's the 3/4 that Tees off to 1/2 and 1/2, used at the final branch off:

enter image description here

In our bathroom there's a 3/4 feed for hot and cold, and after the first branch off it's all 1/2, so that's an option too. Subsequent Tees are then all 1/2 1/2 1/2.

These reducing Tees come in different configurations: some are a 3/4" 90 deg with a straight 1/2 Tee-off.

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There are reasons that they are not readily available. And it is because they shouldn't really be used in most cases.

Having 3/4" water pressure times 2 (hot/cold) is going to blow out filters and gaskets for toilets and sinks which are not really manufactured for that much water pressure.

I had a sink at my old house - which had bad water pressure in general - and basically took out all of the prohibitors (filters/flow valve) so that the water flow was as much as possible. It was for sure too much when all the way up. And that was 1/2"x2.

You hook 3/4"x2 to a faucet and chances are you will blow the innards out over time and it will either clog (calcium plus things not in right position) or it will just allow the whole jet out. Which will be like washing your hands with a fire hose. I have walked into public/business bathrooms and you can tell within 1 second if someone ran 3/4"-1" to a sink. Water is everywhere and people are scared to turn sink on. Its not the faucet's fault because it might have help at first until its gaskets were blown.

For a toilet it is the same deal. You will be replacing the fill valve all the time if you don't regulate the 3/4" flow (even though its just cold). They simply don't make these sorts of things for that much water.

Now can you find a NASCAR toilet to take in that much water... one powerful toilet. Sure. Can you find sinks that push out water like that OK? Sure. I just bought a basin faucet made for high flow. And I got the 3/4" shutoff valve the same place I got the faucet - local plumbing supply.

So the answer is - you do need to unless you are going to install special faucets and toilets that can handle the water pressure or that you can ensure that you will regulate the water pressure using the shut-off (which is not a good idea).

Note: You should be installing 3/4" pex for hot too. I don't even count a toilet into plumbing equations so you have a sink and shower. They could consume at the same time equal amounts of hot and cold. I see no reason why you would install a smaller hot line. This could cause issues with a shower valve especially the ones with anti-scold mechanisms.

Basically if you install like this someone is using the sink. They have hot and cold going pretty hard. The person using the shower will have all the cold they want but may run low on hot. Your shower valves natural reaction will be to lower the pressure. Old school valves will just make it cold. So a bathroom should get 3/4" and branched to 1/2". You can branch to 3/4" to shower depending on the valve you get.

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  • I'm not following the logic here. (1) Pressure does not double at a mixing fixture. (2) The pressure drop under flow to one 2.5Gpm fixture through 10ft 1/2in PEX is negligible (maybe 1psi) and won't protect the fixture: if pressure under flow is too high, reducing to 1/2in in the bathroom won't fix it. You'll need a PRV.
    – P2000
    Apr 21 at 18:33
  • @P2000 - it doesn't double, there is a hot + cold. I just installed a basin using 3/4"x2 in a laundry room. If you turn it all the way up you couldn't keep your arm under it for more than a few seconds. Not sure if I am following you.
    – DMoore
    Apr 21 at 18:37
  • maybe I misread what you wrote, but for (1): "Having 3/4" water pressure times 2" And for (2), are you suggesting that too much pressure is resolved by 10ft of 1/2in?
    – P2000
    Apr 21 at 19:07
  • @P2000 - water pressure time 2 = hot + cold. 1/2" waterflow is about 13 GPM and 3/4" is almost double that.
    – DMoore
    Apr 21 at 19:10
  • A problematic pressure in OPs bathroom (with 2.5 gpm fixtures, not 13) will be not be averted by 1/2 PEX to the fixture. Pressure is not an argument to reduce from 3/4; cost is the argument. If he has a pressure problem (which he didn't say he did), a PRV would be the solution.
    – P2000
    Apr 21 at 19:21

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