Chimney condensation in attic

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Permalink Reply by Ben Stallings on January 22, 2011 at 11:26am

It seems to me the chimney is probably cold, being connected to the outdoors.  So the moisture is coming from the surrounding air.  If keeping moisture out of the surrounding air is not practical, I'd suggest insulating the chimney with fiberglass batts with a vapor barrier on the outside.  Does that sound reasonable?

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Permalink Reply by Dave Dysson on January 23, 2011 at 4:28pm

Is the chimney lined? It could be from flue gases from an unlined chimney. Any problem with condensation on the roof sheathing?

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Permalink Reply by Steven Lewis on January 25, 2011 at 1:36pm

The condensation is from the flue gasses condensing inside the chimney.  This will be increase  as the attic temp drops. ths cools down the brick which allows the flue gasses to condense out at a greater rate.  If there is no clay liner or a flexible chimney liner in the chinmey one will neeed to be installed.  

This has been happeneing before but because the attic was kept warmer do to the heat loss through the ceiling it would only have shown up when it got colder outside.  Now that the attis is seperated from the house there is not enought heat to keep the bricks warm so more condensate from flue gasses is present.  

The condensate is mildly accitic (like lemon juice)  It will turn any paper products a dark chocloate brown after a while.  This is one way to tell the difference between a roof leak and condensate.     

 

All gas furnaces produce water vapor as a by product of combustion adn need to be addressed when furnace, water heaters and such are changed out-   You will need to recommend a chimney liner.

http://oee.nrcan.gc.ca/residential/personal/chimneys.cfm?attr=4  the link will give you a explanation, even though it is canadian, they expriance the problems much more than warmer climates

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