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Housing - New Build: Twin-Walled Flue

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  1.  
    • CommentAuthorCerisy
    • CommentTimeOct 18th 2012
     
    Has anyone experience of sealing a twin-walled s/s flue that's passing through an air-tight barrier? The Selkirk website talks of requiring at least 50 mm clearance from anything combustible, but how to make it air-tight?

    Thanks, regards, Jonathan
    • CommentAuthorRobinB
    • CommentTimeOct 18th 2012 edited
     
    Our flue goes through plasterboard cut as close as possible and the small gap filled with red fire rated sealant. The insulated area is mineral wool and there is a purpose made silicon rubber flange stuck down with the same sealant to seal the flue to the top surface i.e. roof side (in our case EPDM for the green roof* so nice and flat and easy). I also considered vermiculite for the insulation around the flue. Hopefully it's airtight top and bottom.

    I could not say for certain this is how it should be done but it seems to work.

    * I stopped the planting short of the flue and put a band of gravel in that area as I'd heard of dried out vegetation catching fire on green roofs. No chance of that around here it's always lush and green!
    • CommentAuthorCWatters
    • CommentTimeOct 18th 2012
     
    Most makers of twin wall have a variety of fire stop or similar sealing flange for use where the flue goes through a floor, ceiling or roof eg to cover the 50mm gap.

    Perhaps try this company. They were helpful when we needed parts for a flue.

    http://specflue.com
    • CommentAuthorCerisy
    • CommentTimeOct 18th 2012
     
    Thanks guys - stress levels back down (especially as we finally found a helpful scaffolding company over here in deepest Normandy!!).

    Kind regards, Jonathan
    • CommentAuthorfinny
    • CommentTimeOct 18th 2012
     
    The best twinwall product for this detail I have found is from Holland, Metaloterm Ontop Iso block, designed for low energy/passive house to solve this detailing issue.
    Not cheap tho:cry:
    • CommentAuthorchuckey
    • CommentTimeOct 18th 2012
     
    I hope your flue is a type 2 - gd. 904 stainless steel inner -wood/coal, and not type 1 inner = gd. 316 SS for gas.
    Frank
    • CommentAuthorCerisy
    • CommentTimeOct 18th 2012
     
    We are in Normandy Frank - the only gas is tanked, very expensive stuff!! The artisans assume it's wood burning unless told otherwise!! We do know of some Brits that import coal from Holland (if I remember correctly!) - weird! We can harvest our boundary trees and it should virtually cover our needs for future winters in the new house!

    Our local roofing contractor is a great guy - honest and very experienced.

    Jonathan
    • CommentAuthorSprocket
    • CommentTimeOct 18th 2012
     
    What is twinwalled?

    We have balanced flue in a near passivhaus airtight building... we got 2.0 on our last 50Pa test just after the building became airtight (so I epxetc to do better when it is all finished).

    That wasn't particularly awkward.... Is twinwalled something different or did I break the law somewhere?
  9.  
    Sprocket. 2 common types of twin-wall flue for solid fuel stoves.

    1. Retrofit flexi-liner in 316 or 904 grade stainless steel. Literally one tube inside another, but with a very small gap. This is designed to hide inside a chimney, and you definitely would not have it on show!

    2. Insulated rigid S/S flue, for use where (usually) you do not have a chimney, or to terminate above the roof where there is a chimney breast but no stack. Approx 50mm gap between tubes, insulated, if I remember rightly, with Rockwool.

    Re RobinB's ref to mineral wool, I am 90-something% sure that Rockwool is fine and glass fibre isn't, in terms of the heat from an uninsulated flue. (Edit: although from the context RobinB's must, I think, be insulated twin-wall)

    Nick
    • CommentAuthorRobinB
    • CommentTimeOct 19th 2012 edited
     
    Thanks for the clarification Nick, it is indeed insulated twin-wall,and it does look like the gap between inner and outer is filled with rock wool.

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