Insulate "dead air" space with Roxul?

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SharpMaul

Member
Hearth Supporter
Oct 27, 2009
10
SE and NWL Mich
This might be a touchy subject…only my third post so please forgive me my relative stupidity. I've searched and can't quite find this answer.
Prepping my 15 ft masonry FP chimney 12X12 crock lined for a PE Super insert. Installing full length 6 inch SS liner, nearly a straight shot to the stove. Made the block off plate and insulated the smoke box cavity above it rather loosely with Roxul. This area is rather tall and tapered up to the crock liner and it is fully packed w/Roxul. I have bunch of Roxul left. I was going to just pack it around the top of the liner (under the top plate) as is suggested on many posts here.
What I haven't seen discussed is packing the entire length of the liner in the 12x12 crock with Roxul. Seems like most folks in my situation would leave this area open for 'dead air' insulation. This seems intuitive but I thought I should ask, If Roxul is OK above and below, why not in the middle? Between the top plate and the smoke box that is already packed w Roxul is only about 7-8 feet of 'dead air' space around the liner. I have plenty of Roxul left to fill this area.

My perspective on using Roxul…correct me if I'm wrong,…..although it's not rated like Kaowool, it will be just fine above the block off plate UNLESS you have a chimney fire (which I'm not planning on!. This chimney will be cleaned twice a year, once in the middle and again at the end). If I did have a chimney fire, after cooling I would pull it all out, liner too, for a thorough inspection and repack.

Why wouldn't Roxul be appropriate in the middle dead air space so you end up with a fully insulated area around the liner?
 
If it is it not rated like Kaowool, what is it rated? I thought it was similar, just another type of rock wool. I guess the idea is to have something that will be just fine above the block off plate IN CASE you have a chimney fire, not UNLESS. You plan exactly for what you're not planning on.
If it's an exterior chimney I would fully insulate. If it's interior, not a biggie. I think most people do the top and bottom because it's hard to stuff that stuff all the way to the middle.
 
I don't plan on having a car crash, but I still wear my seat belt.

From their web site: "Roxul stone wool resists temperatures up to approximately 1177°C (2150°F)"

Don't know how that compares to kaowool
 
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