Minor B Vent Bleeding - Cold Climate Attic

[Mike Lamb]

It is very rare that I don't see some kind of moisture or bleeding at the B-vent connections in attics. Is this something you would just note if it is minor, but not recommend that it be evaluated further? Is it something you would just consider normal for a cold climate?

[inspector57]

I'm not a cold climate but trying to understand. What do you mean by bleeding? I take "bleeding" to mean liquid or staining coming from one side of a product to the other such as a stain on a ceiling that "bleeds through" and becomes visible again even though the surface has been painted. Pretty much the surface would have to be porous. For a pipe I can't wrap my head around "bleeding" unless clay or another porous material. I can understand condensation or a bonafide leak. What am I missing.

[Jerry Simon]

What do you mean by bleeding?

I believe he means flue gases are condensing in the attic flue section in cold weather, and the moisture is bleeding out of the attic section flue pipe joints. In most cases, join the club; normal, and doesn't always cause problems.

If the leakage is severe enough (and one has to judge by the degree of flue staining/water marks on drywall below/related leakage down at the furnace area), then one can construct an insulated chase in the attic around the flue pipe; this will help keep the flue warm in cold weather and promote a complete flue gas draft.

[Mike Lamb]

Right, condensate leak at the vent connections. I always see at least some drip marks in the attic. They are often minor.

Someone installed an insulated flex duct around this vent no doubt to deal with moisture. I know insulation should not touch the vent but this will probably work.

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And then there is always this method.

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