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Insulated double wall b-vent

At a job and noticed the last 3' of the double wall flue leaving the boiler and entering the chimney in the basement was wrapped with about 2" thick unknown insulation type which was covered in white plastered cloth.
It looks like it was recently done and I have no reason to think this was asbestos wrap, but I don't understand the purpose of insulating b-vent in the basement?
Any insight for the need to do this? They store stuff under this area in the basement so maybe someone thought they could limit contact with the flue pipe to boxes and stuff if they wrapped it up?


  • Bob Harper
    Bob Harper Member Posts: 897
    It's illegal. B-vent is listed for a 1" air space. As for B-vent used as a connector, the IFGC, NFGC and NFPA 211 all prohibit covering connectors with anything including insulation, foil tape, etc. Keeping the vent wrapped will result in markedly increased temps. which is a fire hazard. It doesn't matter what the material is, it must come off.