Plumbing – Should I replace the trunk-and-branch setup with a PEX manifold


My house is plumbed using PEX trunk-and-branch, with the main 3/4 line coming in, splitting off to 3/4" to the hot water tank, and then a 1/2" trunk that all the other branch supplies tee off from. Hot water is the same, with a 3/4" line coming from the tank and splitting to two 1/2" lines.

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The pressure changes when you are using a faucet or in the shower are very noticeable as other fixtures are used, particularly with the washing machine.

I need to do a couple of changes anyway (including adding an outside tap), am both experienced with and have all the tools for PEX, and don't mind spending a couple hundred dollars on this. How much of a difference will I notice if I:

  1. Replace the 1/2 "trunk" lines with 3/4"

  2. Replace the 1/2" trunk lines with a PEX manifold

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I'm just looking for someone's experience/anecdotal evidence that it would not be a complete waste of time/money to do this.

Best Answer

If you increase the diameter of the branch you also increase the time it takes for you to get hot water. In my climate I also like to get ground temperature water so having large branch lines increases the amount of water I have to dump before I get rid of the water in the pipe from the supply entrance to my faucet. This also wastes heat as the branch lines will have hot/cold water and heat or cool the wall spaces - eventually heating or cooling your house.

I like the manifold arrangement but one quick thing to try would be to just plumb the washing machine into the end of the branch line. I this this would allow the other fixtures to have pressure preference over it.

The other thing I'd do is eliminate the crazy 90s if you are redoing a section. The plumbing might look neat but you loose significant flow when you make sharp turns. Really the best way is spaghetti with gradual bends.