Replacing failing copper with PEX

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Old 12-19-17, 02:31 PM
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Replacing failing copper with PEX

I purchased my house two years ago and have now patched 6 pin hole leaks. The leaks have been very random, some in straight runs and other at joints, but have all been in the cold water line. I am now looking to replace everything with PEX. I have a few questions but will give a description of my plumbing layout first....

-2 Story house
-Kitchen (sink, fridge, dishwasher), laundry room (washing machine) and half bath (sink, toilet) are on first level
-Master bath (two sinks, tub/shower combo, toilet) and spare bath (one sink, tub/shower combo, toilet) are on second level
-Both bathrooms upstairs are directly over the kitchen but all plumbing in the house is basically in one quarter of the house footprint
-Currently have well water with 3/4" water supply
-Water heater has 3/4" water supply
-Before all water lines enter the house it goes down to 1/2" supply line
-Both full bathrooms and half bathroom is supplied from the same 1/2" supply line from under the house

I hope that is a decent description to get a layout in your mind so you can hopefully help me with my questions. I want to install a manifold under the house but do not want to do the "home run" style installation where every fixture has it's own supply line. I want to be able to shut off each room individually per the manifold. My manifold would have a hot and cold shutoff for each room, Master bath, Spare bath, Half bath, Kitchen and Laundry room. They only manifolds I can seem to find all have 3/4" inlets and 1/2" outlets. Here are my questions...

-Can I supply each of these rooms with a single hot and cold 1/2" supply and branch off to each fixture as needed?
-Is it ok to branch off using 1/2" lines to go to the fixtures?
-Is this even a sensible way of thinking?
-Does this go against codes in any way?

Any suggestions, questions or comments would be greatly appreciated.

-
 
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  #2  
Old 12-19-17, 03:42 PM
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I am not a plumber. However, it makes no sense to run a 3/4" supply line to the house and then reduce it to 1/2" before entering the house. I would want a 3/4 " trunk line throughout the system with 1/2" branch lines to each fixture.
 
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Old 12-19-17, 04:25 PM
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The existing piping in the house was ran with all 1/2" excluding the main line coming in. I also cannot find a manifold with 3/4" outlets.
 
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Old 12-19-17, 05:35 PM
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I'm not sure why you need a manifold with 3/4" outlets unless you want to run 3/4" to each fixture. I normally run 3/4" trunk lines around the house and T off with 1/2" to each fixture. So, the 3/4" trunk line acts sort of like a manifold. Each fixture has it's own dedicated 1/2" tied to the 3/4" trunk lines. If you want to use manifolds then you'd have 1/2" lines coming off the manifold to each fixture.
 
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Old 12-19-17, 05:49 PM
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I want the manifold to turn off rooms, not individual fixtures. Example would be Master bath would only have one supply line and then branch out to the fixtures but the supply line would have to be 1/2" from the manifold. If each fixture had its own supply, just the master bath would have seven supply lines going to it. That's a bit much for a renovation project. The way I want to do it would only have two supply lines. It's all currently plumbed with 1/2" now but wanted to update if something else is better.
 
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Old 12-19-17, 08:25 PM
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There's nothing wrong with your plan. A 1/2" supply to each room should be sufficient as long as you're not running a high volume (multi-head) shower. Remember, each supply line to the faucet/toilet is only 3/8" anyway. I would probably hesitate running two rooms (2 bathrooms with a tub/shower) off one 1/2" line... though there are lots of houses out there that run the whole house on a 1/2" line.

You can always build your own manifold too with some brass nipples, fittings, and valves. I would usually say copper, but considering the issues you've had, brass would do better, and probably would end up around the same price as a decent prefab manifold.
 
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Old 12-20-17, 02:42 AM
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Before all water lines enter the house it goes down to 1/2" supply line

This is the comment that is confusing everybody!
 
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Old 12-20-17, 05:47 AM
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I personally do NOT like to have a entire bathroom, especially a larger master bath, fed by a common 1/2" line. I believe it leads to the dreaded change in shower temperature when someone in the bathroom flushes a toilet. Much of this has been mitigated by modern anti scald shower faucets. Still, when installing new I don't want to go half arsed.

The water line feeding your house should not be 1/2" at any point. If re-doing the piping inside the house replacing the 1/2" on the main line would be my first priority.
 
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Old 12-20-17, 08:21 AM
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Zorfdt, I would only run one room on each 1/2" supply line and then branch to each fixture with a 1/2" line. Do you have a link or example of the DIY manifold? I am willing to build my own if I can find something with 3/4" in and 3/4" out. Then I would run 3/4" trunks from the manifold under the house to each room and then branch out with 1/2" to the fixtures.

Marq1, I have 3/4" line feeding the house but before the pipes enter the walls to go to the rooms they reduce down to 1/2". The line that feeds all of my bathrooms (2 full and 1 half) are all fed from a single 1/2" line that starts from under the house. This 1/2" line is T'd off of the main 3/4" line and runs to my half bath, then up the wall to the second floor and is then T'd to the two full baths. To me this is incorrect on how to plumb a house but that's how it was done 37 years ago. I hope this makes more since now?

Pilot Dane, The main line from the well to the house is 3/4" and then reduces to 1/2" before entering the walls. Currently the master bath is a very small bathroom with two vanities. In the next 5 years we hope to have an addition built on to the house to connect the house to the detached garage and this will accommodate the ability to have a much larger master bath with separate tub and shower. I would much rather feed this room with the appropriate size pipe now so it's less wasted money down the road. Does that make since? At that time we also plan to add another half bath in the bonus room.


So I guess I have kind of talked myself out of using the prefab manifold with 1/2" feeds to each room. Does it make better since to build my own manifold or just install multiple T's with shutoff's under the house and run separate 3/4" trunk lines with 1/2" fixture feeds to each room? The only reason I want the shutoff's under the house is so I can isolate individual rooms. I will still install the emergency shutoff's at each fixture like a traditional trunk and branch system.
 
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Old 12-20-17, 07:41 PM
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Here's an example of a DIY manifold (from the interwebs)


This one takes up a lot of space, could be condensed into a smaller space if you want. The loop is intended to ensure good pressure to all the takeoffs... I'm not convinced it's necessary.
 
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Old 12-20-17, 08:06 PM
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If I did something similar to this, would you recommend a traditional trunk and branch to each room or a single line to manifold and then to each fixture. The second manifold would not have shutoffs, just for distribution.
 
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Old 12-21-17, 06:40 AM
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Also, since I will be in a 5 foot high crawl space, how should I go about mounting a DIY manifold? I would not go with a loop system as I cannot see a benefit to that either. Should I build some type of drop down "wall" from the joist and mount all the valves to that? The only walls under the house are the perimeter walls and I do not feel that would be a good option.
 
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Old 12-21-17, 08:15 AM
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Just mount it to the bottom of the floor joists. There is no reason it must be mounted vertically.
 
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Old 12-23-17, 10:42 AM
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Thanks for the help. I will skitch out a layout and post up before I start the demo.
 
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Old 12-23-17, 11:54 AM
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After more research it appears all my upstairs hot water should be 1/2 supply to reduce wait time? So why is 3/4 for cold so important?
 
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Old 12-30-17, 07:09 AM
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More cold is typically used than hot. It's the whole flushing the toilet and running the shower at the same time.

In my opinion, a single bathroom is fine on 1/2" pipe unless you have a super-duper shower setup.
 
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Old 01-03-18, 12:33 PM
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Zorfdt, so you would feel that 1/2" cold and hot would be ok for each upstairs bathrooms? I dont mind running larger pipes but dont want to wait 5 minutes for hot water to reach them.
 
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Old 01-05-18, 10:54 AM
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I don't see any issue with 1/2" pipe to one standard bathroom. (with a second 1/2" run to a second bathroom). That's how most bathrooms are plumbed anyway.
 
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Old 01-09-18, 02:10 PM
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ok. So then I could use the 3/4" in and 1/2" out manifold? I plan to run one 1/2" cold and one 1/2" hot to each bathroom and then branch them out to each fixture within that bathroom. This is what I was originally planning until I got caught up in all the 3/4" supply lines.
 
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Old 01-10-18, 04:15 PM
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That's how I would do it.

If you need a 3/4" run somewhere, you can branch out before you get to the manifold.

That's why most (all?) manifolds are 1/2" outputs. If you're going the manifold route, there's really no need to go bigger.
 
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Old 01-16-18, 12:48 PM
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Thanks! I know for a home run system the 1/2" is fine but that's just not very practical for my needs. Now if these copper pipes will hold on a little longer so I dont have to do this in the freezing cold under the house.. haha.
 
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