The house has a gas water heater with no electrical connection. I'd like to replace it with an electric hybrid (heat pump) water heater that requires a 240v 30A circuit. Some of the newer hybrid heaters only need a 120v circuit by dispensing with the backup resistance heating element, but that doesn't really change my fundamental question of running wire to add a circuit upstairs.

Is it allowable to run a 240v 30A line beside a cold air return duct up to the 2nd floor attic? Can it touch the duct, or is space required between them? I should be able to drill a hole for the wire in the corner of the connecting space (think round flexible duct in a square space). It'll be trickier to fish 8AWG between floors that way.

A somewhat related question: Is there a minimum required distance between power wires and natural gas pipes?