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DIY Forum >> Building Questions >> Cap disused 6” flue chimney
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Message started by Lectrician on Aug 13th, 2021, 8:04pm

Title: Cap disused 6” flue chimney
Post by Lectrician on Aug 13th, 2021, 8:04pm

My 1978 house has a brick chimney from a boiler cupboard out through the roof.  Inside the brick chimney is a 6” concrete flue.

The boiler has long been decommissioned.  The cupboard isn’t used, but as we’re having a new kitchen, we’re intending to put a proper door on it, and use it as a “pantry”.

The chimney was for an old gas boiler, previously oil.  The top has a metal top, but moisture does find its way in when it rains.

I intend to put a circle of celotex top and bottom of the flue, and was hoping to cap it with something like the below, but can’t find it in 6”.

[gallery fullsize]Lectrician/1628881252.jpeg[/gallery]

This isn’t my chimney, but it’s the same.

[gallery fullsize]Lectrician/1628881377.jpeg[/gallery]

What’s available to cap and prevent rain on windy days entering?

Is capping with celotex top and bottom ok? Thinking of sweating?

Cheers.




Title: Re: Cap disused 6” flue chimney
Post by woodsmith on Aug 14th, 2021, 9:09am

If you are never going to use the flue again I would take the chimney down completely as they are a weak point in the roof as regards water penetration. We had ours taken down years ago and it wasn’t too expensive.

The one in the photo looks to have had the pot taken off and a gas flue fitted, this is going to make it more awkward to cap off as you do need to allow some ventilation. You can seal it at the bottom with celotex but not at the top so an option would be to reinstate the chimney pot and then you can use a cap like the one in your photo.


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