We need to run NM electrical wire in the ceiling from an unfinished area of the basement through to another room. The problem is that the adjoining ceiling between the two rooms has been sealed off (with plywood) so that there is no easy route to run wire from one area to another. The ceiling joists underneath the plywood run directly across the intended path of the wires.
However, there is a cold-air return duct from the heating system running between the two rooms....it would make a perfect and easy conduit for the wiring. Is this a safe thing to do?