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insulating type B vent pipe

tamojentamojen Member Posts: 1
I have a 100K btuh hydronic boiler in my garage for baseboard type heating.  The type B vent pipe runs horizontally across the garage for about 20 feet (2-45’s and 1-90) then goes vertically up about 25-30 feet to the roof.  It was inspected upon installation, and I know it is just barely meets the code for horizontal to vertical ratio.  The boiler vent hood it beginning rot from condensate.  I assume the flue gases are condensing because of the vent pipe configuration. I believe that the two most obvious solutions are: (1) move the boiler closer to the vertical; (2) or install a power venter to assist the venting process.  My question is: Can I insulate the horizontal run to maintain the internal temperature of the flue gases so that the “chimney effect” pulls the gases up to the roof before condensing takes place.  Is there a safe product to do this? Would it even work?


  • SparrowSparrow Member Posts: 4

    Check out Unifrax FyreWrap here is the link to their site. great products.

    I'm still not sure if it would work due to the lenght and turns you have, but check them out anyway
  • Bob HarperBob Harper Member Posts: 732
    insulating listed pipe

    Sorry but you cannot wrap B-vent or any listed venting with insulation. Only chimney liners may be wrapped and only the part inside the chimney. The listing on b-vent is based upon a 1" free air space around the vent. When you wrap it, the heat signature of the vent changes as do surface temps. of surrounding combustibles. You also obstruct the exterior of the vent from inspection, which results in the vent going for years rotted out undetected. What you are allowed to do as long as the vent mfr. does not expressly prohibit it would be to encase the vent in a weatherized soffit at stated clearances but with the enclosure open to breathe and using listed pass-throughs for combustible wall penetration at both ends. This will tend to keep the vent warmer in the garage portion but you will need inspection access hatches at every joint. Same for above the roof. If you have several feet of vent exposed above the roof, your condensation may be occurring up there. Constructing a weatherized chase is an acceptable solution.

    You can mechanically vent it by attaching an exhaust fan at the termination interlocked with the gas control so the vent is under negative vent pressure but never under positive vent pressure.

    What is the avg. Rh% in the CAZ? A soggy house translates to a soggy vent.

    Do you have any combustion analysis numbers? If not, you should.

    How about you Delta T? If the boiler is extracting too much heat per pass, you may need to adjust your pump pressure or bypass.

    Is the CAZ subject to depressurization?

    The venting numbers you provided suggest this may not meet the code allowed lateral offset of 75% of the total vent rise.

    Any shrouds, obstructions, or adverse local wind effect at the vent termination?

    Has the vent been inspected internally? A damaged inner liner can impede venting.

    Has anyone put screws into the outer casing of the B-vent? If so, that section is essentially not insulated and voids the 1" clearance to combustibles.

    Recommend combustion analysis by certified pro and Level II chimney inspection.

  • unclejohnunclejohn Member Posts: 931
    In my area

    We have the 1 1/2 times rule which means you can run 6" vent 9' horizonal and 4"

    6' h. So seems to be your way over the max and it should have never passed
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