When the house was built, 3 radon pipes were installed between the basement and the attic. They are 6" PVC plastic are completely within the walls of the home except for their ends. Only one of them is used by the radon sub-slab system.
I need to get get some 120 volt electrical wiring between my attic and basement. Can I legally repurpose one of the radon pipes as an electrical conduit? I'm located in New Hampshire, United States. I'm not sure what the electrical code would say about doing so.
If I can do so, do I need to use a flexible electrical conduit within the radon pipe, or can I just run the Romex through the radon pipe with no additional shielding?