My house is over 100 years old and the cold air returns are simply sheet metal nailed between two joists.
I know that when running romex though holes bored in the joists according to the National Electrical Code I'd need to run type "MI" if wiring through the cold air return joists.
I was wondering it it would be OK to run conduit across the /outside/ of the return? I know that romex can only be run through holes in the joists.