Single Wall vs. Double wall vent pipe [Archive] - InspectionNews

David Banks

03-08-2008, 10:49 AM

Jonathan. I got this from Bob Harper the resident expert on such things and keep it handy. Great info.

To identify B-vent, first simply look for the listing sticker. Single walled pipe does not carry a listing sticker. Next, look for the 3/8" bead rolled into the pipe at both ends of each section. Single walled pipe does not have such beads (in general. Some pipe does have it as a depth gauge so be careful). As John Arnold noted, the male end crimp is indicative of single walled pipe. B-vent uses some sort or twist or snap lock mechanism and is not crimped. Single walled pipe is smaller in diameter than B-vent. Not always readily apparent until it abuts B-vent. B-vent is made with an aluminum inner liner and galvanized steel outer casing. B-vent is made to only go male end up if you use the listed components properly. There is nothing stopping you from rigging single walled pipe male end down, which is often done to contain condensation. All it takes is a 5 blade crimper and voila'. The female end of B-vent has the two pipes evident if single walled pipe stuffed into it. The only time you should see a female end is actually the draft hood connector only. You should never see the male end. If the B-vent is properly joined, the joint will overlap sufficiently for it to seat at a ring or indentation in the pipe.

Vent connector clearances:
gas single walled- 6"
B-vent- 1"
Oil single walled-18" unless listing states 9"
L-vent- 6-9" per listing except for pellet venting
pellet L vent-1-3" depending upon listing
wood single walled-18"
wood double walled close clearance -6"
No single walled connectors outside the thermal envelope such as attics or crawl spaces. Too much condensation and weaker draft.
__________________

One inch from B-vent
Six inches from draft hood
Twelve inch rise off hood min.
Draft hood connector
venting secured to draft hood

Bob Harper