Chimney Sweating

2 Nov 2012
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United Kingdom
I have a problem with a damp brown patch round an unused chimney in an upstairs bedroom. The flashing has been checked and renewed, there are no broken tiles and the chimney pots have been fitted with cowls.

However the brown stain is still spreading, another roofer has had a check and reckons the problem is the chimney sweating and it's because the previous guy installed gas cowls:

View media item 81288
He wants to put in some proper cowls that will help prevent the chimney sweating - does this sound right?
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Does the chimney have a vent inside the house to aid air circulation?
IMO it needs a vent inside to create a flow of air and thus stop the 'sweating'. Normally sited at the bottom of the original fireplace or wherever the lowest point is.
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That I can't say. To me they look like terminals fitted to a liner - if so you need someone with more expertise than me on the subject. However as you also have an air brick it would suggest that the stack is capable of venting if you provide some air flow from another vent.
You need to check the copex liner has been removed from the flues the liner would be attached to the gc1 terminals! if thats the case the flues are not vented.

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