Shower mixing valve and continuation of supply line

[Jordan Duff]

New to the forum and to plumbing. Live in an old house, built around 1900. Three bathroom sinks, two toilets, two shower/tubs, kitchen sink, dishwasher, washing machine, and utility sink. Eventually (maybe in a decade) I hope to add another full bathroom....
Virtually all of the plumbing is 1/2" galvanized. My plan is to tear out all of this and do main runs of 3/4" pex, branching off to 1/2" pex at each fixture (probably just tying in to the existing 1/2" galvanized below each fixture for now). Most of the pipe will be fairly easy to get to if I avoid the short runs where the pipe goes through the floor to the fixtures.

I am going to tile my shower on the main floor and while I've got the wall open I definitely want to replace the galvanized in that wall cavity. There are two pairs of supply lines, one pair for the shower and another that goes all the way up into the attic to service the bathroom on the second floor. My thought here was to take out the two lines, and just have one pair of 3/4" going straight up through this wall cavity. I would branch off each 3/4" with 1/2" for the shower mixing valve on the main floor, the remaining 3/4" going up would service the second floor bathroom. I've uploaded a pretty crude drawing to try and illustrate.

Is this the best way to tackle this?

 

[Jamesplumbing06]

Your drawing didn’t come thru. But keep doing homework. Galvanized pipe is hard to work with. don’t leave 6” just because you can’t get to it. It all needs to come out. But first do the main from meter. Pressure will force the trash in old galvanized into the new pex and then your right back to square 1. 3/4” main with 1/2” branches is the way we do most residential homes. So your on track. Do not let anyone talk you into a “dresser coupling”. They don’t work and you will regret covering up in wall.

 

[TomFOhio]

You got the right idea...... Like James said, if its a small amount of galvanized you would be best to get rid of it and have
new pipe right to the fixture.

 

[Jordan Duff]

Thanks guys. I’ll see if I can go ahead and do pex all the way to the fixtures.

About the shower wall cavity - am I thinking of it right?

There are currently two pairs of supply lines in the cavity. One pair for the shower and another that goes all the way up into the attic to service the bathroom on the second floor. My thought here was to take out the two lines, and just have one pair of 3/4" going straight up through this wall cavity. I would branch off each 3/4" with 1/2" (horizontally) for the shower mixing valve on the main floor, the remaining 3/4" going up would service thesecond floor bathroom. Is this the way to do it? If so how would you recommend shutoff valves for the shower? I think there may be room between the 3/4” line and the mixing valve on one side but maybe not on the other.

 

[FishScreener]

If you have one line and tee off to the shower, everything down stream may have a profound effect on the water pressures seen at the shower.

If you’re changing to pex it should effectively give you more room in the bay, because you can staple the lines for upstairs to the studs, and have them out of the way.

And, the recommendation is to run to bathrooms with 3/8, or 1/2-inch lines, to decrease the lag time before your hot water gets there.

 

[Jordan Duff]

And, the recommendation is to run to bathrooms with 3/8, or 1/2-inch lines, to decrease the lag time before your hot water gets there.

Are you saying I shouldn’t have a 3/4” hot water main that runs to the upstairs bathroom? Or that I should branch off my 3/4” main in the crawl space with 1/2” to my main floor shower? Or both? I do appreciate the help you’re giving this newbie.

 

[TomFOhio]

I would run 3/4" from your 3/4" main line all the way up to the bathrooms and branch off with 1/2" to the faucets.

 

[Jordan Duff]

Very good. My plan was to run 3/4" lines up from the crawlspace into the attic, branching off with 1/2" lines to hit the shower mixing valve on the main floor. I've uploaded a picture below of the main floor shower mixing valve to try and show this, the thick lines being 3/4" lines (hot and cold), the thin lines being 1/2". The arrows at the top just represent the fact that these same 3/4" lines would continue up and supply the bathroom above. Is this how you guys would handle this? If so, how would you recommend shutoffs at this main floor shower?

 

[FishScreener]

The best way to run pex is a distributed manifold system. This allows smaller diameter runs, which require less water to get fresh water to the individual taps. A 3/8-inch line, will get hot water from the heater to the tap, with 1/4 the water and time of a 3/4-inch line.

 

[Jordan Duff]

I do think the manifold is the way to go, but I may have to stick to something more basic since I’m a newbie. Thanks for all the advice. Hopefully the system in my crude drawing will work.

 

[FishScreener]

The manifold and individual runs to each fixture is actually simpler for a newby. It is really straightforward to size a line to an individual fixture, and you have no fitting losses.

 

[jeffnc]

Actually a manifold w/ home run is easier and more basic in some ways. Less time usually, fewer joint connections = less money on parts, less time making connections, more reliability in terms of potential corrosion or leaks, and better water flow overall. You should seriously consider. It costs more in pipe, but that is offset by previously mentioned, and also you are running 1/2" instead of 3/4" so that helps offset also. All the connections are then visible - all the ones on the manifold should be somewhere easily viewable and accessible and where a leak wouldn't do damage anyway, and the connections at the fixtures will obviously be visible.