Re: Building Manifold for use with PEX
1/2 inch copper is rated for something like "seven fixture units." A fixture unit isn't necessarily one per fixture; a bathroom sink is one, a toilet is two, and a bathtub is three, for example. I don't remember how many fixture units 3/4" copper is rated for.
I would recommend using 3/4" copper. This will help you to avoid pressure drops, for example when someone starts filling the bathtub you won't lose pressure in the kitchen sink.
Ideally, you should have a 1" line from the meter to where it branches off to the water heater. At that point, you can run 3/4" pipe to your manifolds.
Of course, this is all subject to the building code used by your local authority and the number of fixtures in your house. My suggestions are based on an average 2000 square foot house with 2-1/2 baths.
The "Senior Member" designation under my name doesn't mean I know a lot, it just means I talk a lot.I've been a DIYer since I was 12 (thanks, Dad!). I have read several books on various home improvement topics. I do not have any current code books I can refer to. I was an apprentice plumber for two years.