First time seeing a electric and gas water heater in utility room. Any issue with this configuration.
My guess would be an they were unwilling to increase the size of the vent.
or the electrician was cheaper than the plumber or gas line installer?
Dual Fuel! clearly a belt and suspenders installation to ensure hot water no matter what fails.
Can’t see where the gas shut off or the drip leg, should they not be on the WH side of the drywall?
Ditto for PTR drain - is that 1/2" pipe?
Are permanent mounted gas appliances allowed to be connected with movable appliance flex where you are?
All of this would be wrong for Alberta, YMMV
Not so much. You have 50 gallons of cold water ahead of the hot water if the gas unit fails in the serial installation. If it were parallel and you could shut one off that would work.
My guess is it’s added capacity for when it’s needed (e.g., when the kids are visiting). Flip the switch and shut off the up stream unit when there is less demand for hot H₂O