Pipe Sizing New Remodel

I am remodeling my master shower (48x34). I would like to put in a rain shower, a main shower, a hand spray (or use hand spray a main) and 4/6 body sprays. We have the biggest residential tankless hot water system you can buy (9.4 GPM) in the basement and the shower is on the 2nd level. We have a well system with pressure set between 60 and 80 psi. I have quite the water filtration system that includes a contact tank, an iron filter tank, a charcoal filter tank and a water softener tank- all heavy duty but I'm sure this impacts my pressure. The pressure out of our shower head isn't that good - could be the shower head as the pressure out of the garden hose is perfect and the bathtub on the same 1/2 line gushes water like it has no restrictor.

Anyway that was just a little background. I want to put in the best possible system since I am doing everything myself. I want to maximize the pressure and I'm not worried about amount of water used - although I do understand I am limited to a 2 inch drain. I'm thinking I need to run the entire 3/4 inch pipe (not far away) into my shower and have 3/4 inch piping all they way to the diverter which will then deliver 1/2 to each outlet.

Anyone see any problems with this or have concerns? I am having a hard time finding a complete system with my required specs. I may have to piece meal this together the best I can. Comments/tips welcome.

i would pipe the whole thing in 3/4
where a valve is 1/2'' install 3/4x1/2 reducers on each side of valve

How many gallons per minute are all these heads that are going to be on at the same time using? Or trying to use?

I'm not entirely sure as I haven't picked out the heads. I would guess 2-4 GPM rain shower, 2.5 GPM shower head, 2.5 GPM had spray and 4-6 GPM body sprays. Depending on my valve setup, only up to 2 outlets would be used at one time. If I went with four separate volume controls then I guess potentially they could all be running but don't see a practical need for that.

BTW having a heck of a time finding an all in one value system with a 3/4 mixer and 4 outlets that operate on a 3/4 inch stack (mixer output).

We just re-did our master bath. One normal head and one rain head. The house has 3/4" copper. 1/2" feed to each head. The shower head with the restriction taken out will hurt you. The rain head is still restricted. Rains pretty good, but both together, not so good. My pump is set 75/95.

For what it's worth, I've used the rain head twice in one month.

I'm assuming the 1/2 feeds are independent and not on the same line? What do you think your total GPM is for both? Curious what your shower head was before and after the restriction.

My master shower and tub are on the same 1/2 line and I can fill the tub (all the way open to a nice gush) and take a decent shower at the same time. If I can do that I don't see why I couldn't run another 1/2 line off the 3/4 for another 4-6 GPM. I ran a test with the garden hose that is on the other side of the house from my main - so about 60 feet with I don't know how many bends. That got me between 8-9 GPM running 1/2 at around 70 PSI. Master bath isn't as far (about 30 feet) but it is one more level up from that garden hose outlet.

BTW do you have 3/4 coming in from the well or an inch/inch and a quarter?

1-1/2 from the well to the house. Then right to 3/4". They used to have two ground water heat pumps before changing to forced air. This was all before I bought the house. I was the second owner. I know most shower heads are under 3 gpm. The plumbers can tell you exactly how many gpm they are allowed by code. Some are easy to defeat and some not so much. Look up friction loss charts on Google. They can tell you how many gpm through a given size pipe at X pressure per hundred feet. That might help.

Also that tankless is a certain GPM at certain temp rise. They don't always supply what they say because of the temp rise. If you have colder water coming in it needs to be kicked down to heat to the set temp.

Hadn't thought of that. But with the temps here in Florida, that's not an issue so far. With the copper being in the attic even though it's insulated; a shower at 5M could probably take place without the assistance of any water heater.

LOL. If you put the pipes on the roof like a swimming pool heater you would have unlimited hot water. I'm not far from the well so I think the water coming in is a constant mild temperature for the most part. So GPM in winter vs. summer I would suspect would be pretty similar. We haven't noticed a difference although most the time we don't push the system.