I need to install a fresh air intake for my pellet stove. The flexible metal tube is about 1.5 feet too short. I was going to use PVC pipe through the wall and connect the metal flex between the stove and the PVC. In the install book it says that PVC is NOT approved for the fresh air intake. I want to know if this is because there is a chemical makeup that the PVC outgases (like new cabinets do formeldahyde) and would cause toxic fumes or if its just because they are afraid some idiot would attatch the PVC directly to the stove. So i'm wondering if it would be ok to set it up like I am intending to do or if this is a big No No.