Question: is pvc pipe plenum rated?
Answer: Combustibility & Use in Plenum Spaces: PVC, like all plastics, is classified as a combustible material per ASTM E 136. PVC has low flame spread, but smoke developed ratings may be as high as 900, so PVC will not pass the 25/50 criteria of the ASTM E 84 test and may not be installed in plenum spaces.