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Clay Thimble Clearances for Safe Installation

Post in 'The Hearth Room - Wood Stoves and Fireplaces' started by Taylor Maxson, Dec 3, 2012.

  1. Taylor Maxson

    Taylor Maxson New Member

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    Nov 8, 2012
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    Howdy Folks,

    I have done some poking around about this question, and wasn't able to answer it to my satisfaction via my reading. I apologize in advance for any redundancies.

    Refer to the photo of the existing clay thimble in our wall, which I've just busted open:

    We're planning on installing our Vermont Castings Intrepid II through this wall. I read that the minimum safe clearance from this 6" ID clay thimble to the nearest stud is 12", so that we would need to build a 32" box around the thimble in all directions. The actual clearance from the outer edge of the thimble to the studs, as it was done by the past owners of the house, is only between 4-6" from the clay thimble to the studs (see picture). But my question is, can we just remove the studs around the brick wall patch so that there is no wood within 12" of the thimble. It would seem to be an obvious, "yes", yet I'm not sure we can safely remove some of these studs (load bearing?).

    The main question is, what would be the best option for passing through this wall, without spending unnecessarily or creating overkill in terms of cutting out studs, etc. The stove itself will be connected to a stainless steel, smooth wall liner in the chimney.

    A licensed chimney sweep came by this morning, and said it was "already safe" but that if I wanted to, I could take sheet metal, insert it between the brick wall patch and the closest studs, and make a sheet metal protector over the studs. That sounded like a total mountain jerry rig, and I don't trust it.

    I mentioned the idea of using the SAF T THIMBLE which has zero clearance as a wall pass through, and he thought that was a waste of money.

    Thoughts on the best course of action?

    Finally, we want to have the closest clearances between our stove and the wall behind. If we screw cement board (tiled Durock, etc.) directly onto the studs to form the wall behind the stove, will it technically be "non-combustible" or would we still need to have a wall shield with a 1" gap to get the closest clearances (our manual says 9" from a "protected surface" with our heat shield and double wall pipe) to the wall? In other words, should we just go ahead and put drywall back up, and then screw in a wall shield an inch from that drywall? Or will durock acting as the wall surface make this redundant? DSCN0380.jpg

    Thanks,

    Taylor

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  2. begreen

    begreen Mooderator Staff Member

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    Cementboard directly on studs offers little protection. It needs the ventilated 1" air gap behind it to be effective as an NFPA211 protected surface.

    That thimble and chimney are too close to the studs. The stove manual should show thimble reqs. Here's an article in case it doesn't.

    http://www.hearth.com/econtent/index.php/articles/passing_a_chimney
  3. chimneylinerjames

    chimneylinerjames Feeling the Heat

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    You can use double wall stove pipe, that would reduce the clearances to 6".
  4. Taylor Maxson

    Taylor Maxson New Member

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    Thanks for the response. Are you referring to using double wall stove pipe as the wall pass through, or from the stove to the thimble? If it's the former, would this mean busting out the clay thimble (which is 8" OD) and mortaring a section of double wall pipe there?
  5. chimneylinerjames

    chimneylinerjames Feeling the Heat

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    As long as you keep the brick as is and keep the dry wall away 6" from the pipe, 8" from the top, it will be fine installing the stove pipe into the terra cotta thimble. But if you want to cover up the brick with dry wall then you would have to do something else.
  6. DAKSY

    DAKSY Patriot Guard Rider Staff Member

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    I don't believe that's an option when connecting to a liner in the chimney. There is no way to go from Double-Wall to Single-Wall. To reduce your clearances, you'll have to remove the terra cotta & go with an approved wall pass thru that has allowances for connction to a tee on the Flue Side of the thimble.
  7. chimneylinerjames

    chimneylinerjames Feeling the Heat

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    You would just need to crimp the snout on the liner and it will slide inside the male end of the double wall pipe.
  8. Taylor Maxson

    Taylor Maxson New Member

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    I called my liner manufacturer, and it turns out they just started carrying an adapter for the liner tee snout that does allow the snout to connect to double wall pipe without crimping. So I'm a bit closer to my answer, though I still need to figure out whether I can safely cut the studs near the brick wall patch to get safe clearance from the soon-to-be double wall pass through. Thanks again for the response.
  9. chimneylinerjames

    chimneylinerjames Feeling the Heat

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    If you use double wall and leave the brick there that would be fine. Clearances with no masonry, just air, is 6". You could even slide in a piece of sheet metal between the bricks and the studs. That would be fine.
  10. DAKSY

    DAKSY Patriot Guard Rider Staff Member

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    Loc:
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    You can cut your wall studs, but if it IS a bearing wall, you will hafta add a header above the 12" clearance zone, similar to what you'd do if you were adding a door or window. That will include "jack studs," tied into the remaining wall studs on either side, to support the header. Standard framing techniques.
  11. Sithspawn

    Sithspawn New Member

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    Loc:
    Newfoundland, Canada
    Taylor,

    Here is My suggestion, Insulated Wall Thimble :)

    I'm not sure if there is a Dealer in Your area for ICC Liner. You can have a look at this item here :

    http://icc-rsf.com/main.php?t=chem_produits&i=46&l=en

    [​IMG]
    Basically, this attaches to Your brick Chimney with the liner end going into the masonry chimney & usually attaches to a liner tee. The other end acts like prefab chimney, this a keeps Your clearances to combustables going through the wall & connect Your stove pipe to. This product looks great when it is finished.

    I hope this helps

    Cheers,
    DAKSY likes this.

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