Wall thimble too short for basement wall

[Fullcurl74]

Hello all, new to posting, but been reading as a guest for the last year. So much knowledge on this site!

I'm currently installing an Enviro wood stove in my basement, which is causing me to go out through the basement wall and then up outside of the house with stainless insulated chimney.

My question involves the AmeriVent thimble my dealer sold me. It only extends to about 9 inches, but my basement wall is about 14" thick, leaving a 5" gap between the two thimble halves. My dealer said this is ok as long as I frame in a box going through the wall to prevent any insulation (or other combustibles) from every getting within 2" of the insulated chimney pipe that's exposed for the 5" between the two halves of the thimble.

So I framed in a pass-through box using hardie-backer cement board (see pics). In my mind, this would accomplish the goal of never allowing combustibles within 2" of the chimney pipe. The cement board "tunnel" is about 13 1/2" square with 6" insulated pipe (8" o.d.) going through the center of the box.

However, searching this forum for others who've encountered the same problem, I see that everyone recommends fabricating a connector with sheetmetal to bridge the gap between the two halves. Is this necessary??

Thanks in advance..

 

[EatenByLimestone]

When I ran into this, I ended up buying a new piece of insulated thimble and cutting it to fit. Not the cheapest option but I felt better with all of the insulation.

 

[webby3650]

Just cut a piece of sheet metal to extend the thimble. Easy, run into this often. I would think it’s unnecessary since you enclosed it with cement board.

 

[Fullcurl74]

Just cut a piece of sheet metal to extend the thimble. Easy, run into this often. I would think it’s unnecessary since you enclosed it with cement board.

Yeah I was wondering if I still needed to add sheet metal since it's fully boxed in now. I don't know how hot it would get inside that box.