I’m new to PEX plumbing in that I’ve finally switched over to it fully but only when doing retrofits. I have my first job now to plumb an entire house with it and I have some questions on what is the best design.
The design calls for two bathrooms which share a wet wall. The sinks are back to back, toilets are back to back and tubs are back to back with the wall common to all fixtures.
I’ve been taught that the best PEX runs are home runs off a manifold. In a situation such as a back to back bathroom arrangement, is it still best to do homeruns to each fixture. That is, a cold and a hot run from the manifold to each sink (a total of 4 runs to the manifold), a cold and a hot run from the manifold to each tub (a total of 4 runs again) and a separate cold for the toilet to each toilet (total of 2 runs)? This would make a combined total of 10 runs of pipe to service both of these bathrooms. Does that sound right and make sense? Sounds like an awful lot.
I hear you can do a traditional trunk/branch (as you do in copper plumbing) but I heard the manifold system is a much more appropriate design.
I also heard they make smaller manifolds where you can run a main branch to service the smaller manifold nearby where you need to branch off it and thought maybe the smaller remote manifold would be best. It would allow only 2 main runs back to the main manifold and then much smaller runs off to the fixtues nearby.
Also, I”m used to computing pipe size on fixture units. Does that change with PEX? Like would you run 2 1″ PEX lines to the remote manifold (a hot and a cold) and branch off with 1/2″ pex to the individual fixtures?
Replies
You could easily combine the cold feed from the sink and toilet, but keep the showers hot and cold lines seperate. The whole point of the home run is that the shower NEVER spikes due to pressure variation. Another point is that you don't need run a ton of water before it turns hot, but that's probably not an issue here, just a side benifit.
For the bathroom setup you are talking about, each shower gets 2 lines. Another two lines can be shared by each sink, it's unlikely hands will be washed at the same time, and a sudden cold or hot spike there isn't going to make anyone jump out of their skin. These share the cold with the toilets. I count a total of 6 lines going to this bathroom.
Rebuilding my home in Cypress, CA
Also a CRX fanatic!
If your hair looks funny, it's because God likes to scratch his nuts. You nut, you.
That makes sense to me and settles the issue. I assume,however, that to split the cold between 2 sinks and 2 toilets I'd just use Tee fittings like a trunk/branch in use today, correct?I count 6 lines also based on what you said. Does the pipe size matter much though? I mean 1/2" PEX is not really half inch when you use the fittings, it's more like a 3/8 bottleneck with the barbed fittings. Does that really matter? Especially if I do as you're indicating? Like if you would have both sinks on, what's the water flow/pressure like using 1/2" ftgs. Seems like it'd be slow and little pressure?If at first you don't succeed, try using a hammer next time...everything needs some extra persuasion from time to time. -ME
Well, as PEX is pennies a foot, and Sharkbite fittings are easy to use and reusable... I say just mock up a setup in the yard with two sink taps and a toilet. Turn the water on an see the difference in flow. I doubt you'll notice much with sink taps.Rebuilding my home in Cypress, CA
Also a CRX fanatic!
If your hair looks funny, it's because God likes to scratch his nuts. You nut, you.
All the houses here are plumbed with pex using the same sized 1/2" or 3/4" you would find in copper installations. Apart from very minor differences, the finished job is indistinguishable from the way copper would be plumbed. I don't understand why if the two systems use the same size pipes, and are plumbed the same way, people insist pex must be done with manifolds, but not copper.
Prolly has to do with cost. You can't homerun copper and be economical. The advantages of manifolds are it evens out water pressure so there are no sudden drops, which is most appreciable when you're in the shower and the toilet flushes.If at first you don't succeed, try using a hammer next time...everything needs some extra persuasion from time to time. -ME