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ice build-up on "B" vent

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  • ice build-up on "B" vent

    up here, humidity is one of the enemies.

    during the winters our chimneys form ice at the termination. i have removed ice blocks that were probably in excess of 50 lbs.

    as a former volunteer fire fighter and fire chief we would get fire calls for houses where the occupants got smoked out.

    the furnace/boiler kicked-in and all of the combustion products started spewing out of the barometric draft control in the mech. room. the only reason the appliance shut down was because there was so much smoke the cat's eye couldn't detect a flame.

    upon inspection of the chimney, we discovered that the inside lining of the "B" vent collapsed inward due to a ice/water build-up in between the outside and inside jackets.

    the seams on the vent would allow water vapor to to enter the insulation. the appliance would shut down the water would freeze and expand. next heating cycle more water vapor was introduced into the insulation then freeze when the appliance shuts down. a little more water, a little more inward expantion of the inner jacket, and so on.

    over an extended period of time, and dependant on the humidity level inside the structure determines how long vent will last.

    i have seen a 6 or 8" (can't remember exactly) crushed to the point where the actual hole for the vent was no more than 2" (5 centimetres ) in diameter.

    i have also noticed that structures built with modern technology and materials to make them air-tight are more susceptible to ice build-up.

    have any of you guys ever seen this?

    do you think i could seal up the end of the vent with fireproof caulking to prevent this?