Help! This thimble ain't simple!

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New Member
Oct 1, 2020
New England
Dear All,

My first post! Thanks for all the great info I've found here while researching a replacement stove! But now that I've got one I'm running into trouble!

While swapping out our old Firelight 12 for a new-to-me 2012 Jotul F500 Oslo, I discovered the fireclay thimble was cracked and needed replacing. I also realized that the brick surrounding said thimble was not up to NFPA 211 standards (existing clearance to combustibles was only about 1 brick worth!). Please see attached photos (if I am able to attach them, this being my first post).

My chimney guy (who is great, but booked out through January) suggested an insulated wall thimble kit as made by Selkirk/Olympia/Heatfab etc. Being a handy fellow, moderately smart, even though I have never worked with brick, I figured I could at least follow directions and install one as a DIY project before it gets too cold! I'm leaning towards the Olympia but the Selkirk IWT looks fairly easy too. Both these will fit my opening with minimal or no reframing. Maybe there are other models/kits?

My trouble began when I started chipping away removing the brick and the thimble expecting the brick to be only in the wall, HOWEVER the brickwork runs from the room side wall all the way back and is built into the structure of the chimney. As such the running bond pattern of the bricks runs parallel to the run of the thimble. So, instead of finding a nice flat outer surface to my chimney, I have an irregular surface of partially sticking out and/or broken bricks!

My question is: how do I create a flush surface upon which to mount an insulated thimble kit without affecting the integrity of the chimney? As in, I'd rather not knock bricks out of the chimney itself!

Can I square off the bricks where they are sticking out, mortar in some brick where needed to create a surface that is flat but juts out from the chimney by 2.5" or so? I understand I need a surface that would accommodate the flange of the insulated thimble kits (secured by mortar and tapcons) I'm looking at.

Or might there be other solutions? I talked to our local building inspector and he suggested those insulated thimble kits or even using double, or triple wall listed stove pipe used as thimble with 2" air gaps around?

This is tight quarters! Wall's rough opening is only 14.25" square. Not much room to get many tools in there! I can sort of get my angle grinder with masonry cut off wheel in there. I have hacksaw with masonry blade, but that may take me till January to cut through the bricks to make them flush...

Interior cinderblock and brick Chimney built in 1990 (?) with tile flue in good shape
Accessed through 8" combustible wall +3" airspace between wall and chimney surface
6" fireclay thimble (removed)
Opening in flue is 6"
Distance between bricks either side of where thimble was is 7.75"

Been in the house 3 years and we burn about 4 cords a season, so I want this to be safe for the family, and to pass inspection!

Grateful for any suggestions!



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