Background: Sorry for the long explanation, but I think it's worth providing everything up front. We are remodeling the upstairs master bathroom. Due to some nasty floor joists I've already had to tear up all the subfloor anyways, so access to the water lines and drains is not a concern. The shower and toilet aren't getting moved but we are moving the location of the double vanity. Not sure if it matters, but we are only talking about an 80 square foot area. My question is about the best way to re-run my water lines (polybutylene that needs replacing anyways...)

There are two diagrams below. Diagram A is how I plan on plumbing everything just based on how it was done previously and moving the vanity. However, we experienced low pressure at the faucets and when both my wife and are using the bathroom we would like maximum pressure. Diagram B is my attempt to "loop" the hot and cold lines by tying them back in, hoping that would keep even pressure no matter what is being used any given time: shower, toilet, faucets...

Question: Will Diagram B work or not? (dotted lines are where I would loop back to the beginning)

Diagram A

Diagram B

  • In what way would you expect this loop to improve water pressure? If you've got 30 PSI coming in at the top left, you've only got 30 PSI to work with, no matter how many ways it's split. – FreeMan Aug 2 '20 at 21:52
  • Okay, maybe I'm asking about flow rate and need to update my question? – Jake Schmitz Aug 2 '20 at 21:54
  • You will decrease the resistance in the lines to the sink (basically like going to larger diameter pipe) so it should theoretically increase the water pressure slightly, but I doubt it will be a noticeable pressure increase unless you drop from 3/4” to 1/2” on the supply lines right before the toilet or something. – statueuphemism Aug 2 '20 at 21:58
  • @statueuphemism lines are already 1/2”. Sorry for not noting that earlier and thanks for your input – Jake Schmitz Aug 2 '20 at 22:14

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