I’ve never seen a water heater with an overflow pipe.
The PEX material is suitable for use as a T&P relief discharge, of course, there are many other factors to consider before deciding it’s OK as implemented.
Is that a direct CSST connection to the gas control valve?
In my area Blue PEX is not allowed on a water heater relief valve. Blue is cold water only. We use Red PEX, CPVC plastic and or metal only as a downspout. Blue PEX and PVC plastic is not rated for hot water.
someone is feeding a bunch of hokum
red, white, and blue PEX pipe are all rated the same
Uponor PEX carries the following hydrostatic temperature and pressure ratings.
200°F (93.3°C) at 80 psi
180°F (82.2°C) at 100 psi
120°F (48.9°C) at 130 psi (½" tubing only)
73.4°F (23°C) at 160 psi
In accordance with ASTM F876 Standard Specification for Cross-linked Polyethylene (PEX) Tubing, the excessive temperature and pressure capability for Uponor AquaPEX® is 210°F (99°C) at 150 psi.
Should be 1" PEX due to fitting restriction. That’s the code in my area.
Rated PVC and any other material approved for use as distribution piping is acceptable for a TPR pipe. This plastic pipe however is too close to the draft hood/flue.
BA I don’t make the rules I just follow them. Water temp from a relief valve can exceed 210F;-)
PVC schedule 40 in my area is not allowed for a downspout as the rating is 180 degrees F
As Chuck said, that is NOT an overflow pipe.
And you are in California.
PEX is not listed as an approved material for TPR discharge pipe in the California Plumbing Code. Though there is a provision for “other” which leaves a bit of a grey area.