Need advice on how to keep pressure.

[Ghost 60]

We are turning an old huge bathroom into two smaller baths.
All of the supply need to be replaced in the house. It is mess of copper to galvanized to Pvc and back.
How do I run the water so that I won't get an interuption of pressure in the shower when other water is turned on in the house?
The two showers will be four feet from each other and will be used at the same time. They are about 20 to 25 feet from the water heater.

We have a family of seven and have to keep the water very hot to have enough for everyone. I just don't want anyone scalded or chilled out of the shower if water is turned on in another part of the house.

[jadnashua]

A couple of things. Pressue will be flakey until you can get rid of the galvanized.

All new shower valves have anti-scald technology to help prevent that. They adjust the balance between hot and cold as the pressure drops on one side to keep the temperature fairly even, so replace the valves. At a minimum, it will have a pressure balance valve built-into it.

Personally, I prefer an enhancement on that, a themostatically controlled valve. It does about the same thing, but you can set the desired temp, and winter to summer, it stays the same.

To extend the amount of hot water available, you'd need to do two things: turn the thermostat up AND install a tempering valve on the outlet of the WH. That is an adjustable valve to mix some cold into the hot to 'temper' it to a safe value. They generally come from the factory set at 120-degrees. But, if you are going to replace the WH, you should consider sizing it to the expected use. It's still not a bad idea to run the WH hotter, since at 140 or above, typical bacteria and virus can't live (there are exceptions, but they're rare).

[Gary Swart]

I certainly hope you misspoke when you said you have PVC water pipes in your home. PVC is not acceptable for interior water pipes and especially hot water pipes. OK for drains. The galvanized has to be very old as that has not been used for a number of years and is probably corroded internally to the point of being clogged. You very well may be looking at a repiping of you home.

[Ghost 60]

We will have to replace all the incoming pipe. Yes there is pvc and cpvc and a truck hose...LOL (not kidding). I have been gathering all the replacement parts, a few at a time and just put in an 80 gallon WH set on He!! to make sure to have enough hot water. I am just not sure how to pattern the water flow to my best advantage.
I am pressed at the moment to get the second bath up and running. There are too many people here to have just one toilet!
I have been trying to bypass some of the worst parts of the Frankenpiping as I find them under the very small crawl space. When I found the truck hose I "knew" I had to redo the whole thing.
Is the key to pressure, keeping the pipe large and then T-ing off with smaller pipe as you pull from supply?

[jadnashua]

Generally, if you run 3/4" to the area, then tap off with 1/2", you'll maintain decent pressure.

An alternative to that is to use PEX. You can use home runs from a manifold, or run a larger trunk, then use a room manifold to supply the local points of use.

Of the PEX systems available, Uphonor seems to have the lock on the better system. Some would debate that, but it does seem to work well. As with many, the quality of the workmanship plays a big part in it as well.