Help with a shower supply lines install

My wife and I are remodeling our bathroom.
One part is to replace the fiberglass tube/shower surround with a 60X34 tile spa shower with 4 body sprays, a hand held shower and a rain shower head.
The fixtures we are using are by Moen and require 3/4" supply lines.

My problem is the cold water supply is 3/4" through the house but is T 'ed off to 1/2" at every fixture in the house, Kitchen, Bathroom sink, and Tub/shower.

The hot water supply line is 1/2" from the furnace to every fixture.

I think I can replace the T reducer with a 3/4" T for the shower cold supply.

But, can I install a fitting to go from 1/2" up to 3/4". If I can will that cause me any other problems? Or do I have to install all new 3/4" pipe?

A 3/4" pipe can flow nearly twice as much water as a 1/2" pipe. If you calculate the area of the pipe ppening (pi * r^2), you'll see why. Trying to flow more than about 6gpm in a 1/2" line will lead to erosion. So, it depends on what your specs are on the devices. Because the radius is squared, a little change results in a much bigger area, lower restrictions, and higher flow capacity. Just bumping the 1/2" pipe back up to 3/4" to make the connection won't help (much) getting more water there. High restrictions will decrease the flow, and therefore the performance of the shower.

If the inlet piping to the WH is only 1/2", you may need to go way back to where it is 3/4".

What is the max gpm of the shower fixtures you bought and what else to you think may be flowing at the same time?

valve

I have absolutely no problem with piping a 3/4" valve with 1/2" piping, knowing that the actual ports in the valve have a smaller area than the 1/2" pipe does. Whether you upsize from the tee or not, and whether it would make any appreciable difference, depends on how far it is from there to the valve.

So, it's ok to go from 1/2" up to 3/4" without a problem?

At the shower, if you turn everything on, how many gallons/minute does it use? If it is over 6gpm, I think you need it to be 3/4" all the way.

Course, you won't be using all hot, so as HJ says, it probably won't be a problem. But, if it is trying to flow much more than that, you could have problems, especially if there are other hot users at the same time.

hot

If "other hot users at the same time" cause a problem it would be because of something ahead of the tee, so it would not make any difference what size the pipe to the shower valve was. In fact the effect could be less with the smaller pipe because of a smaller demand.

Here are the ratings of the fixtures.

The handheld is rated at 2.5 GPM
The rain shower head at 2.5 GPM
The body sprays at 1.75 GPM each.

If all are running it's a total demand of 12 GPM.

I don't really think we will ever run all at the same time.
So I think the potential max demand at any one time may be 9.5 GPM (rain shower and body sprays)

Will a 1/2" supply lines handle the potential max demand?

There are no other hot users, except maybe the dishwasher. We only have the one bathroom.

No, it won't

nhmaster said:

No, it won't

Click to expand...

If it won't, how can I solve this problem?

As I said earlier, a 1/2" pipe can only safely support about 6gpm. You need to replumb things with at least 3/4" all the way from the supply, through the WH to the shower. Also, think about the size of the WH, if you have all of that running at the same time, you will need a quite large WH to keep up with the demand. Anything else you try will not give you the full functionality of the shower system you want...it's a premium system, and requires proper support systems. Maybe more than you wanted to spend, but anything else would be a compromise.

For that volume you are probably looking at a 1" supply to the bath group, depending on incoming pressure and length of run.

Now I can sleep better. Thanks everyone for all your great info. and advise.

I've decided this job is beyond my skill level, so I contracted a Pro Plumber to upgrade the supply lines from 1/2" to 3/4" and do all the rough in work for our new spa shower.