Can I use PVC pipe for the combustion air intake?

Reznor does not approve the use of PVC pipe for combustion air intake. Reznor only approves the use of the concentric venting, which is not compatible with PVC. Attempting to vent non-concentric can lead to pressure imbalances which would cause the pressure switch to intermittently turn the unit off. If you have any further questions, please feel free to give us a call. Thanks!