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Fixing improperly installed Metalbest chimney

Post in 'The Hearth Room - Wood Stoves and Fireplaces' started by Andreas, Feb 17, 2013.

  1. Andreas

    Andreas New Member

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    Previous owner of our house improperly installed a metalbest chimney system. He squeezed the pipe through 2 floor joists between the 1st and 2nd floors, there is 10.5" between the joists instead of the required 12". To compensate he created a makeshift heatshield using aluminum flashing tacked to the sides of the joists with fiberglass insulation between the layers to protect the joist from heat of pipe. I attached a picture that is hopefully helpful. I've monitored this over the winter here and it seems fine, but I'd be concerned about how it would stand up in a chimney fire. I see two solutions, the easiest being to create a better heat shield by attaching a thin piece of aluminum to the joist but with a ceramic spacer to hold it off the joist so it can properly dissipate the heat. Option 2 is opening up the ceiling and properly blocking off the floor joists. This will be tricky as I'd have to block off 2 joists and the next one in line is the rim joist making it very awkward to re-frame properly. Has anyone created a heat shield to reduce the clearance of metalbestos from 2" to 1"?

    Attached Files:

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  2. KodiakII

    KodiakII Feeling the Heat

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    Don't think that is a good idea. Clearances are there for a reason and I don't recall any provisions for heat shields reducing them in my chimney installation manual. You are either going to have to go with a through the wall installation or take your pipes down and box in your floor joists so you get the proper clearance. So much for inspections eh?
  3. Rich L

    Rich L Minister of Fire

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    You might be able to place Roxul around the pipe.It can with 2000 plus degrees of heat.
  4. Andreas

    Andreas New Member

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    The danger of packing fiberglass or rockwool around the chimney pipe is that it attracts dust and the dust can then combust, bad idea......needs to be air space, that's why I was going with a heat shield idea similar to the way a rear heat shield on single wall stovepipe works.
  5. EatenByLimestone

    EatenByLimestone Minister of Fire

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    Can you move the chimney?

    This is a spot where you should do it right or not at all.

    Too many things can go wrong when your loved ones are asleep.

    Matt
  6. webby3650

    webby3650 Master of Fire

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    You absolutely cannot use any kind of heat shield or insulation to reduce the clearance on a class A chimney. It's tested to a 2" MINIMUM. Meaning at the very least.
    Other than reframing the opening, the only option would be to replace the chimney with Dura-Tech from Simpson. They offer a reduced clearance box that measures 10"x10". I think Excel also has a 10" ceiling box. I don't know why these boxes are exceptable, but they are tested and approved.
    Chimneys problems are zero tolerance, the only way that you know there is a problem is when your house is on fire! Don't risk it!
    pen likes this.
  7. Andreas

    Andreas New Member

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    Moving isn't possible without considerable demo and rebuilding through several layers, roofing, cathedral ceiling framing and insulation, etc.....also stove is in small room, moving out from wall further doesn't work.
  8. Andreas

    Andreas New Member

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    I think I came up with a good solution, since I only need an extra inch or so on each side I'll attach a minimum 6' long piece of joist stock the same width on each side of the chimney with sub-floor adhesive and screws clamping the two tightly together, and then cut out the 12" required for clearance.
  9. webby3650

    webby3650 Master of Fire

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    I though it was a cathedral ceiling? How will you do this?
  10. Andreas

    Andreas New Member

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    Sorry, must not have clarified, split level saltbox, woodstove is in lower level, chimney passes flat ceiling to second level than through cathedral ceiling to roof. The joists b/t first and second floor are 12" o.c. hence the tight situation, cathedral is no problem as it fits through the 16" o.c. rafters no problem.
  11. webby3650

    webby3650 Master of Fire

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    Then it sounds like you have a plan. Good luck! Just make sure you keep the 2" clearance, you will be fine.

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