Minimum supply size for 2 shower heads

[Rossn]

As part of my remodel, I am looking to add a second shower head to my shower... it will actually use the existing 3 way valve that was intended for body sprayers. The existing Kitek Pex-Al-Pex will also be removed.

In copper, and in PEX, what are the minimum sizes that can be used for the hot water supply?

I am asking about minimum size because it is about a 33' run and currently (5/8" PEX home run) it takes too long for hot water to reach.

Cold water supply pressure at the mechanical room is 60-65 psi.

Thanks for the guidance!

 

[Rossn]

I should mention that if I use PEX, I'd be using the Uponor AquaPex

 

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[Jadnashua]

A shower head can flow up to 2.5gpm. So, two of them, essentially 5gpm. That can pretty much max out a typical 1/2" valve when fed by copper. I'm guessing you have nominal 1/2" pex, which would be 5/8" OD. Because the wall thickness of pex is greater than on copper, it typically has a little less volume capacity. The difference is that it tends to have less internal friction because it doesn't need as many fittings. There's a difference between static pressure on a line and dynamic pressure (when water is flowing). The faster it tries to flow, the more friction, the less pressure there is at the end. When there's no flow, it's the same (except for possible height differences) at the source and the point of use.

To maximize your flow, even to a 1/2" valve, you might find it works better to use 3/4" pex, and convert to a 1/2" fitting at the valve. That would effectively give you the same ID as 1/2" copper with a little bit to spare.

To minimize the time it takes hot water to arrive, a hot water recirculation system may be your best choice along with making sure your lines are well insulated.

 

[Rossn]

Sorry - didn't see this earlier. Thanks, for the input, Jim! Current is a 5/8" pex home run (not 1/2"), however it is also supplying the lav, which it would not be in the future (to overcome the heat delay issue there, I would supply it via 3/8" from the supply to the lav that is about 12' away). The other end of the house is a very long run, and I am using an on-demand recirculation pump for that end. However, it's hard to stomach the extra $500+, maintenance, and energy loss for a recirc pump that will only serve one fixture, if it's possible to avoid. My guess is that the second shower head might get used 20% of the time, or less and it would definitely be a 2.0 or less GPM.

Tough call as to what to do here and would be great to hear from anyone who installed two shower heads off 1/2" PEX or 1/2" Copper

 

[Jadnashua]

Most 1/2" valves seem to be rated at 5-6.5gpm. A showerhead could use up to 2.5gpm, so with two of them, depending on which ones, you might have less than optimum results. To work best, you want to be able to supply more volume than the heads are designed to use...that's what lets the pressure stay high out the jets. Think of a hose without a sprinkler on the end...it doesn't go far. Throw some restriction on the end, and the sprinkler can jet the water quite a distance, but the pressure is the same. Put a splitter on the hose and feed multiple sprinklers, and their performance decreases. That's one reason why lawn sprinkler systems tend to be in zones to let the heads work to optimum. Using copper, the Copper Institute calls for a maximum velocity of 5fps for hot. With 1/2" copper, that's 4gpm. Use more, friction goes up, it can literally start to erode the inside of the pipe, and it can start to have some flow noises. While pex can support a bit higher velocities, the ID is smaller. In the winter, with the potentially super cold cold supply, you'll be using mostly hot, and only a little bit of cold to get showering temperatures. So, things might work well in the summer when the hot/cold mixture is a bit more even, but may not in the winter when it leans allot more towards hot for the same outlet temperature.

 

[ande8414]

Hi! Curious what was the outcome of this project? I just started a new thread with a very similar situation and wonder what worked for you? Thanks!

 

[Rossn]

Unfortunately, I won't be much help to you. I am in the middle of a massive remodel, and have just finished the heating, and will be moving to the plumbing soon. And, I did decide to go the propress route, meaning copper, using 3/4" with a recirc pump and a dedicated 1/2" return line.

 

[ande8414]

Okay sounds awesome! Good luck!