Multiple shower head supply volume question

Hi, I was hoping that someone could give me some advice on some plumbing for a new shower I'm working on.

We're planning on having 2 (High-Efficiency) shower heads plus a rain maker shower head as well. Each shower head will be controlled by their own mixing valve, and off of one we'll have a diverter for the rain maker.

The supply to the house is 3/4 inch, and that's continued into the water heater and back out, so I do have 3/4 lines I can tap off of, but I was planning on using 1/2" pex for the entire shower. Am I going to have a flow issue with only using 1/2" or should I just do everything in 3/4"? Should I do 1/2" and do a pressure balance loop between the valves? Please advise

Thanks!

The real question is how many heads will be running at the same time. If all of them, you'll probably be disappointed running it in pex, especially if you use 1/2" which has a smaller ID than 1/2" copper. Once you know the max flow, check it against the valve you want to use. 1/2" valve can flow about 5gpm with 1/2" copper supplies. A 3/4" valve can probably flow over twice that. Depending on the heads, you may not need it, but I think I'd run the 3/4" up to the valve, and if you don't go to a 3/4" valve, reduce to 1/2" there.

That's what I figured. I know pex is smaller id than copper, especially when you get into using the crimp fittings as well.

At least 2 shower heads would be running at one time, but probably not all 3.

The flowrates are critical to sizing as mentioned by Jim earlier. However, even if the "high efficiency" means 1.5 gpm or so, you should probably size if for the 2.5 gpm rating of standard modern showerheads. In that case the total maximum flow would be 7.5 gpm.