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    • CommentAuthordeniance
    • CommentTimeOct 4th 2013
     
    hi everyone, im new here and hoping to learn how to block up my redundant flues correctly.

    chimney stack is on an internal wall, would i be correct in saying that flues should be sealed at bottom to stop warm house air entering and rising to top of stack and condensing,
    then insulated to the same level as the loft insulation, and sealed at top of stack

    or should it be sealed at bottom, insulated at loft insulation level and open at stack (with rain cover)
    or should it be sealed at bottom, insulated at loft insulation level and sealed at stack with brick removed below roof level
    or sealed at bottom, insulated at loft insulation level open at stack, and brick removed below roof level

    any help would or explanations would be great , im hoping to learn, as the draughts the flues make are getting a wee bit cold!!!
    • CommentAuthortony
    • CommentTimeOct 4th 2013
     
    I would take it down above the ceiling and insulate over the top of it, otherwise it will still be a thermal bridge between the house and the loft.

    You could even remove it all the way down to the ground! and gain some additional floor area.
    • CommentAuthorSeret
    • CommentTimeOct 4th 2013 edited
     
    What's your budget?

    In the short term putting a ventilated rain cover on the top and sealing it tight at the bottom will stop you losing warm internal air up it, which is the lion's share of the heat loss. Cheap and easy. After that it really depends on the exact layout of the chimney, your budget, and what your objective is. Are you satisfied with a quick fix that does 3/4 of the job, or are you trying to squeeze every last bit of performance out of the building?
  1.  
    I think its generally accepted practice not to completely seal off chimney voids in case of condensation problems.

    Some kind of air vent would be put in near the bottom.
    • CommentAuthordeniance
    • CommentTimeOct 4th 2013
     
    i dont have a budget, ill do what it takes as long as its right!

    i cannot remove the stack as im using 1 out of 4 flues, the other 3 are sealed off at the bottoms bricked up and plastered with vents, i have sealed these vents air tight and i have covered the 3 pots on the roof with home made stainless steel rain cowls, which have pretty much sealed them airtight.

    however, i have been told that because i have sealed top and bottom i will get damp appearing because of condensation in the chimney.

    my thinking was that if i could stop moist air entering from below it would not condense and if i stopped rain going down that this would not condense also

    but the person who has told me this also thinks that the moisture that was already in the flues from when they open to the rain will evaporate because of house warmth travel up to the cold attic stack above the insulation and condense, i think he may be right, but i thought id ask you guys as you all seem to be really clued in to these things

    my house is stone walls, 120 years old, chimney stack changes to red bricks in attic, attic has 300mm insulation, lime mortar etc, chimney has been rebuilt halfway up in lime mortar and also repointed in lime mortar
    • CommentAuthordeniance
    • CommentTimeOct 4th 2013
     
    i was hoping, or my thinking was that as the cold stack is completely built of lime below and above the roof that this would allow any previous moisture that was present to dry out and all would be well,

    my next step was to remove a brick in the attic and add insulation into the flues the same level as the loft insulation
    so this would leave me with a sealed flue at ground floor(living room), this flue then goes up through 1st floor (bedroom), flue travels through cold attic (insulated inside flue to loft insulation level) then up onto roof stack

    i will leave brick removed in attic above insulation level, would this be enough to ventilate the attic and roof part of the stack? as said, the attic and roof stack are built in lime, rebuilt and pointed in lime above roof level, nice new flaunching, attic is very well ventilated i assume as you can feel wind blowing through it

    i hope this will be enough, and i hope my thinking was correct
    • CommentAuthoreniala
    • CommentTimeOct 16th 2013
     
    Hi, don't know if you have sorted this out now and I don't know if what we've done is actually the right thing from a strictly technical point of view, but it seems to have worked for us. We have twelve flues in our house and I just wanted to keep two of them open for downstairs fires. However we also wanted to retain the original Victorian fireplaces as they were a feature in the bedrooms.

    We fixed expanding metal (the stuff used for plastering) across the base of each flue (slightly up inside so you can't see the metal unless you actually have your head in the fireplace!) and then we filled the whole flue with Vermiculite by pouring it down the chimney pot. We then put clay cowls (with ventilation holes) on the top. This means the whole flue is still vapour open but is warm with no drafts. We did this nearly two years ago and we have no damp or condensation. Four flues are on external walls and six are on internal walls. It seems to have worked in both cases. The chimneys above roof level (and below in fact as we have used lime internally as well) are completely breathable though because they were built using lime and have been re-rendered in lime.

    The beauty of this as well is that because it is loose fill, if we want to use the fireplace or indeed if a problem surfaces after a while all we have to do is remove the grill at the bottom and let the vermiculite out.
    • CommentAuthordeniance
    • CommentTimeNov 3rd 2013
     
    thanks for the help guys, appreciate it
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