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How to seal flue after liner install?

Post in 'The Hearth Room - Wood Stoves and Fireplaces' started by wahoowad, Dec 23, 2005.

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  1. wahoowad

    wahoowad Minister of Fire

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    I intend to pass a 6 inch flex liner through my 8 inch flue, and connect it to a tee pipe. This will leave about a 1 inch gap between the liner and the flue. How can I seal this gap to prevent cold air from passing by it? I know cold air comes down that pipe pretty good if I forget and leave the damper open after a fireplace fire goes out.

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  2. saichele

    saichele Minister of Fire

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    1) there should be a top plate at the top of the liner. Seal that down to the tile with high temp silicone.

    2) you should, although it's ocassionally a point of debate, install a block off plate in the damper around the liner. There are plans for one on the hearth.com site.

    Steve
  3. wahoowad

    wahoowad Minister of Fire

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    I should have been more specific. This is not a masonry fireplace.

    Also, I found the link Steve mentioned but the images in the page are not working.
  4. Mike Wilson

    Mike Wilson New Member

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    I have a full length 6" flex running from the insert through the 5" wide damper. At that level there is a block off plate which is sealed with high temp silicon around the perimeter, and furnace cement around the actual flue. Two batts of high temp fiberglass insulation are beneath the block off plate, held in place by metal wire. At the top of the chimney there is a metal plate with the flue coming through. The plate is sealed to the top of the 12" tile flue with high temp silicon. Approximately 6" over that is a 6.5 foot long by 3.5 foot wide slab of 2" thick slate, capped with approximately 60 pounds of poured cement on top to roll the water off the chimney. End result is that the water runs away from the flue, which is completely sealed on both top and bottom. The insulation prevents cold air from the masonry from spilling down when the insert is not in use.


    YMMV...

    -- Mike
  5. roac

    roac New Member

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    Is there such a thing as "high temp fiberglass"? Isn't all fiberglass insulation without any facing or plastic high temp? Fiberglass is non flammable right? On the pink panther (you know who they are) website they say to use unfaced fiberglass batts around any masonry chimney in the attic since it is non flammable. Just wondering.
  6. Mike Wilson

    Mike Wilson New Member

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    That's what I thought, but others here have said the contrary, so I signed up with their program. Don't know if its a marketing ploy or what, but in my first year I had regular un-backed pink fiberglass in there, and when I removed it to have the flex installed, the pink had turned white for about a 4-6 inch diameter around the flue pipe. It was also pretty hard for about 1" around the flue. Glass melting? Who knows. So I picked up 2 batts of this high temp fiberglass at the local HVAC shop. Different consistency than the prior pink stuff, somewhat thicker, beige colored. Seeing as I was only getting two batts, I didn't pay attention to the cost. Probably was a bit more, but who cares. I checked it about 2 weeks ago when I pulled the cast iron surround off the Jotul, and it was still flexible, same color, and hadn't hardened at all.

    -- Mike
  7. elkimmeg

    elkimmeg Guest

    Mike many did not believe me that the fiberglass melted They thought I was pulling their legs Well you sure found out
    Micore I bleieve it what it called that would be the correct type to stuff in that 1" space One could also cut a sheet metl ring and cutincluding 3 square tabs that can be bent up to screw and hold the metal ring in place
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