PEX Re-plumb...

[NYGIANT]

Long story short - after chasing pin holes in my copper pipes for years, I've decided that a major re-plumb with PEX is my only alternative. Anyway, the leaks have only been in the horizontal hot water pipes so they have to go. I believe the culprit was the old water heater that was in this house when we purchased it almost 30 years ago. Fortunately, we live in a one story ranch and all the plumbing runs through the basement and is mostly accessible. I plan on changing all the old copper up to the point where it turns "north" into the upstairs to supply the various fixtures - this is both because there doesn't appear to be anything wrong with the vertical pipes and most importantly to simplify the changeover.
Now, here's my question and I'm sure there is no simple yes or no answer but I have to start somewhere...
My current system runs off of a 3/4" trunk line that has 1/2" branches to all my fixtures. I plan on using PEX A with expansion fittings to replace the old copper. To make life simpler, can I just use 3/4" PEX to replace everything or should I try and duplicate the existing system using both 3/4" trunk lines and 1/2" branches?
Thanks in advance for any advice you can offer.

 

[Gsmith22]

Look up what is available for fixture connections and I think you are going to find that basically everything is 1/2" at the fixtures. so your choices become 1/2" lines homerun from a manifold, larger trunk to 1/2" branch lines (matching your existing system), or Uponor's logic plumbing. I did the logic plumbing and couldn't be happier. Uponor has tons of brochures on how to do this - search "Uponor residential plumbing installation guide" and/or "uponor plumbing design assistance manual" for more information that you could ever want to know about this. The logic system essentially uses smaller remotely installed manifolds (called multiport tees) that mix the best parts of the manifold and trunk/branch systems.

Also, you may want to consider upsizing the main trunk line by one size in order to maintain the same flow - the internal diameter of PEX is smaller than copper and therefore results in more friction loss (less pressure/flow) as the water moves through the smaller diameter pipe. I had 3/4" copper and went to 1" PEX for the main trunk line stepped down to 3/4" for branches and then used multiport tees that went from 3/4 to 1/2 at fixture groupings. Some areas went from main trunk to a multiport tee with 1/2" connections. I would search out what you want to do and what is actually available and that may dictate the layout (it did with mine).