I have a project planned in the near future. Going to be installing a HE condensing propane combi boiler. The exhaust is planned to go up through the ceiling, into the attic, and out the side of the house. My question is can the exhaust (pvc) come into contact with the insulation in the attic on it’s vertical run through the ceiling before 90ing out the side? Are there any other “clearance to combustible” issues w this type of pvc vent pipe?