Metal boxes in cold-air returns

[jeff48356]

In the past, I've failed a rough inspection due to the fact that I used plastic boxes in the vertical cold-air return spaces on some walls. I didn't know that I needed to use metal ones. But where is the Code reference stating that? I'm not sure if I've ever seen that written.

 

[packersparky]

In the past, I've failed a rough inspection due to the fact that I used plastic boxes in the vertical cold-air return spaces on some walls. I didn't know that I needed to use metal ones. But where is the Code reference stating that? I'm not sure if I've ever seen that written.

300.22(C)(3)

 

[JFletcher]

300.22(C)(3)

Also not allowed is running Romex parallel (along the stud or joist) inside such spaces used for air return... You can cross them perpendicular; exception to 300.22 C