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PEX.....trying to decide how to run

I intend to use PEX tubing to do the plumbing in my 19 fixture home. This is for the obvious reasons of cost and labor. My friend and I will be doing the work.

I heard about 2 options for running the PEX.

1) A manifold system with each line being direct to the fixture.

2) A conventional "copper" system with a couple "main trunks" going through the house and branching off for the different fixtures.

I don't know any cons to either but it does seem that the "conventional" way would be the easiest and least expensive.

Any thoughts?

Re: PEX.....trying to decide how to run

Method 1 requires fewer fittings but more pipe. Nearly all your pipe can be 1/2", which is somewhat cheaper than larger sizes. You can also put a shutoff valve on each line at the manifold, to shut off the water to each individual fixture. The cost of the additional pipe will likely outweigh the savings on fittings. You will also find that hot water will reach the farthest fixtures more quickly, as there will not be as great a volume of cold water in the lines to be removed.

Method 2 requires less pipe but more fittings. If you were paying a plumber to install it, the cost savings on pipe might not balance out the labor costs to install the additional fittings.

Timothy Miller
Re: PEX.....trying to decide how to run

Howdy, either method works manifold saves $ over fittings. Major issue is Pex an sun light on it - huge no no... UV causes Pex to fail Rapidly. New construction here in OR plumbers stub out walls with copper so no UV exposure. Mostly seen manifolds used with in floor heat to control zones.

Re: PEX.....trying to decide how to run

With the manifold system there will be alot of water wasted when trying to get hot water to the furthest fixture. You could install a 'Loop System' to re-cirulate the hot water. But that can also, be a big energy waster if you live in a cold climate and/or the hot water pipes are not insulated.

Also, with the manifold system you will only have to run 1/2" lines to your manifold box. Some condo I have worked on even ran 3/8" lines.

Pex without quewstion is the way to go.

Re: PEX.....trying to decide how to run

i did the manifold system in my house, a copper manifold with shutoffs for each individual fixture in the house. i love it and i even added one extra hot and cold shutoff should i need it for something new. we don't have a big issue with hot water getting to the fixtures but if some of the runs were longer we might. i have one manifold for hot and one for cold. after the manifold was set up it took me about 4-5 hours to get water to every fixture in the house, couldn't have been easier.

Re: PEX.....trying to decide how to run

Just to clear up a common misconception: large diameter pipes does NOT necessarily equal faster hot water.

The larger the diameter of the pipe, the more water there is in the pipe. The more cooled-off water there is in the pipe, the more that will have to be removed to get the hot water there. And since water flow from a 1.5 GPM faucet will be the same with a small pipe as with a large pipe, it will take a lot more M's to get the lot more G's out of the larger pipe.

For this reason, I believe the manifold system will get you faster hot water, IF all the water in the pipes has cooled down. With a branch system, if the bathroom is on the way to the kitchen, and you've recently used hot water in the bathroom, you'll probably get the hot water sooner in the kitchen than you would with a manifold system.

Remember that when you open the hot water tap and let it run, all the water you're dumping down the drain had to be heated at some point, and that's wasted energy.

Doing it either way is fine; you'll just have to make the decision based on what makes the most sense in your situation.

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