A few PEX design questions

I am building a new home, in which I will be the GC. I have experience running pex, and thought I may tackle the supply work in my new home. The pros/cons of all of the layout options have my head spinning. I keep flip-flopping between doing a remote manifold layout and a home-run system. I was wondering if someone would be kind enough to answer a few of my questions/concerns...

1.) My plumbing inspector informed me that in WI, 3/8" sized pipe of any kind is not allowed in walls. This seems strange, since the demand of so many fixtures is less than the amount delivered by 3/8". I suppose that the code isn't always logical

2.) My main concern is energy and water waste, followed by hot-water wait times. I was originally planning on the home run, since the hot water wait for a 3/8" would be so minimal. If I have to run 1/2" everywhere (some fixtures would be 50-75ft away), it may reduce the benefits of a home run system.

3.) When other folks are using remote manifolds, I assume they are using the flow-through type, and basically chaining them all together with 3/4"? Essentially one large loop? This, combined with a recirc pump would help with wait times, but the furthest fixture would be hundreds of feet away. I'm having difficulty finding examples of this type of layout.

If it sheds any light, my house is a victorian, with kitchen and powder on first floor, 2 baths and laundry on the second floor, mechanicals in the basement.

Again, if anyway has a though, I'd really appreciate hearing it......

1) 3/8 branch lines really only make sense in a home run installation, but if your local code won't allow them, then there's nothing you can do about it.

2) Your desires to keep energy waste to a minimum as well as keep hot water on demand contradict each other, so I'll assume you really prefer to keep hot water wait times to a minimum. If you have long 50'+ runs, then a home run installation doesn't make sense. You really only want to do a true home run installation if you want the security of not having any fittings in the wall as well as the ability to isolate each line in case of rupture. You are probably better off going with a traditional branch & trunk or a hybrid manifold setup, and using a recirculating pump.

3) This is where plumbing design experience comes in, and you might want to try and track down an experienced plumber to design a system for you. But beware of who you hire as your proposed installation is not common, so there are plenty of ways to get it wrong.


I am a big fan of a true home run installation, but there are plenty of installations where it is not practical, and the layout of your home may be one of them.

I'm starting to question even using Pex at all. Doing a standard Trunc/Branch with CPVC and a recirculating pump might make more sense. For whatever reason I feel more comfortable with having CPVC fittings in a wall than a Pex fitting. After measuring again, it looks like the furthest bathroom is roughly 60 feet of pipe away. Maybe some on demand recirculating pumps would give me the best of both worlds.