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acceptable block off plate material for zero clearance prefab fireplace?

Post in 'The Hearth Room - Wood Stoves and Fireplaces' started by jblood, Nov 10, 2011.

  1. jblood

    jblood New Member

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    Should this be stainless steel or will galvanized steel be adequate. It will be a ring that is 6" inner diameter (slightly larger than the flex liner) and about 9" outer diameter (slightly larger than the damper opening). Seems to me it could get quite hot as it will be making direct contact with the ss liner only several inches away from where it exits the appliance. What type of sheetmetal are prefab fireboxes typically made of?

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  2. Milton Findley

    Milton Findley Feeling the Heat

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    The zinc coating on galvanized sheet metal begins to boil off at 720 degrees F and zinc fumes are not healthful. On the other hand, we are talking about a small amount, screwed to a large heatsink. My prefab firebox is made of stainless steel.
  3. DiscoInferno

    DiscoInferno Minister of Fire

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    I believe I used galvanized for the blockoff plate for my Fireview-through-a-prefab setup. No issues to report, although mine has more exposed pipe before the plate and the Fireview doesn't get the pipe all that hot, almost certainly never up to 720 at that point. Also, there isn't a lot of direct metal-metal contact, it's mostly furnace cement between.
  4. cmonSTART

    cmonSTART Minister of Fire

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    With such a small gap, personally I would just stuff some rock wool in there and be done with it.
  5. webby3650

    webby3650 Master of Fire

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    X2, it looks like you already got it covered, from the picture.
  6. jblood

    jblood New Member

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    I do have rockwool stuffed in the gap. I would like to put a block off "ring" just to keep the rockwool in place and seal the gap. I cannot find stainless sheet anywhere locally though.

    I was thinking of using some plain carbon steel and paint also, but galvanized or painted steel just seem like a compromise.
  7. webby3650

    webby3650 Master of Fire

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    The whole pre-fab is made of very thin sheet metal, I don't think a sheet metal ring would be any kind of a compromise.
  8. wahoowad

    wahoowad Minister of Fire

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    See if you have any local business that do ductwork. They typically perform a lot of custom sheetmetal work. My local shop hooked me up with some materials and even did a special cut for me that I wasn't sure how to do.

    I would love to see any more pics you have of your installation, now as well as when you finish. Are you going to install a plate to simply cover the gap and let the liner pass through, or are you going to somehow mount the block off plate and then connect the liner to it?
  9. jblood

    jblood New Member

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    I will definitely post more pics as I proceed. I think the blockoff plate will be nothing more than a piece to cover the insulation and keep it in place. The liner isnt going anywhere. It had to navigate two bends within the 8" pre fab chimney and it was a job to get it in. Also it is secured to the appliance about 10" from the damper opening and at the top of the chimney.

    Thanks for hvac tip also. I'll look into that. Seems as though they use mostly galvanized also.
  10. Milton Findley

    Milton Findley Feeling the Heat

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    I have galvanized right by my liner and it hasn't even discolored. I would not hesitate to use it myself. It does not get very hot as it is screwed to a lot of stainless steel.
  11. wahoowad

    wahoowad Minister of Fire

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    jblood - did you terminate the flex liner into a tee inside your firebox? If so, any pics of that?
  12. jblood

    jblood New Member

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    I hear ya but if prefab is stainless, liner is stainless, it seems a shame to introduce galvanized. Having said that, maybe I'm overthinking it....
  13. jblood

    jblood New Member

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    Just found a place that has 26 GA SS 12" x 12" in stock for $8.

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