Can I drill a sample hole in Type B, Double Wall Vent Pipe?
Unfortunately this has become a controversial issue in some areas. The concern seems to be that flue gases will ‘leak’ out of the hole. It is our contention that if flue gases are leaking out of a 1/4 inch hole in vent system which is designed only for a negative pressure, that hole is the least of the concerns….. If you need to, check with your local authority having jurisdiction. We can also provide a copy of a letter from the president of the B-Vent Manufacturers Association which basically says that as long as the hole in the interior liner is sealed, (with a “quality grade silicone RTV”) they don’t “believe that a single hole through B-vent for purposes of measuring draft would affect our UL listing”. In areas where the ‘authority having jurisdiction’ will not allow this procedure, contractors have typically used a short stick of B-vent right off the breeching (pre-drilled), taken tests and replaced the drilled piece with another.
