PEX renovation trick?

[Piercello]

Hello,

I am upgrading my home plumbing by replacing 25 yr old C-PVC lines with a new PEX manifold system.

Everything is easy basement access, except for one pair of 3/4 C-PVC lines that feeds 4 fixtures: a main-floor vanity and a second-story full bath.

And my new manifold has only 1/2 outputs...

Question: can I improve my expected flow upstairs by tying TWO 1/2 PEX runs apiece into the old lines down in the basement, where I can reach them (1/2 PEX + 1/2 PEX teed into 3/4 C-PVC, for both hot and cold), or is that a bad solution? Will it even help? I have the manifold outputs to spare.

Thanks,

A DIY plumber

 

[Riickk]

I'm not a plumber, but from what I remember, two (2) 1/2" pipes carry the same amount
of water as one (1) 3/4" pipe. However, how you'd connect the two to one might be important,
the flow through a Tee (1/2--3/4--1/2), where two flows merge into one might lower the
pressure in the 3/4" line. Maybe some else here knows more.