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chimney liner cap question

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  • chimney liner cap question

    I posted this question on another forum as well; I hope no one minds since I know I'll get good advice here:

    My fireplace and boiler flues exit side-by-side through the same chimney. I just had a s/s liner put in the boiler flue. The installer removed my 14x26 s/s chimney cap (covering both flues) in order to put on the new liner rain cap, which stands too tall to put the chimney cap back on. Can I remove the new liner cap completely and reinstall my 14x26 cage to cover both flues? I need both flues covered, and this seems like a perfectly fine idea to me.

    Thanks for your feedback.

  • #2
    No expert on flues and chimneys here but my first Q is why did the installer remove your one piece cap that covered both flues (which is not a good design) and then leave it uncovered? You ended up with less protection than when you started to my way of thinking.

    The single cap for both flues is bad because the exhaust from one can be drawn down into the other. If only one flues is active then the gasses can bounce off the underside of the cap and fall toward the other inactive flue, and maybe find their way into the house. I may not have explained it too well but that is the danger with your original setup.

    Normally you would have your fireplace damper closed when not in use but after a fire you can't close it right away. It's during this time that exhaust from the boiler can find their way down the fireplace flue and into the house.

    I would call them back and get them to replace the missing cap and screen on the fireplace. I think one should be extended above the other by 12" or more to mitigate the backfeed condition.
    "It's a table saw, do you know where your fingers are?" Bob D. 2006


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