1/2" copper supply with 3/4" PEX trunk and branch

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Toronto, Canada
Hi, I've tried searching the forum for resources but couldn't find I'm looking for. I have two questions and I would love everyone's feedback:

Some context: I'm in Toronto, Canada. I'm renovating my 1100sqft house that was built in 1954 with a 1/2" copper supply line, and I want to avoid the headache and cost of increasing it. There's currently 1 full bath (on the 2nd floor) but a second full bath will be built in the near future in the basement.

- Is it okay to use 3/4" and 1/2" trunk and branch system with PEX straight from the 1/2" copper supply. Or should I keep everything 1/2" PEX. The water pressure in the house is adequate.
- The pipes that supply up to the bathroom from the basement are located behind the furnace. The closest pipe (hot line) is currently 3" away from the supply duct. Is 3" enough space between the duct and PEX with pipe insulation? Relocating it is unfortunately not an option. Attached is an image of the location.


- The bathroom will not be renovated with PEX in a few years, but I would like to know if is it wise to keep the existing 1/2" copper in the walls to the bathroom to avoid demoing walls outside the bathroom. Ideally I would like to replace with with 1/2" PEX, or increase it to 3/4" PEX going up in the walls and branch off to 1/2" once in the bathroom, but that's only possible if I can do it without major demoing.

Thank you,


The Plumbing Wizard
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Bothell, Washington

A two bath home gets a 1" from the street. PEX has a smaller diameter than copper and needs to be sized with that knowledge.
Upsizing pipes helps to future proof your work.
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