# How to insulate a concrete block chimney



## Bob Mariani (Dec 1, 2008)

code requires a 2' air space from combustible materials. I use injection foam which is fire resistant and not a combustible product. Best approach is to leave the required air space and insulate with Thermax foam board on the outside.


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## 21boat (Dec 26, 2008)

In my neck of the woods we use Rock Wool insulation for fireproofing. Its also required between a chimney when the chinnmey is inside a home penetrates another floor where the box framing around that chimney is a fire chase IE Rock Wool stuffed against the chimney and wood framing stops a fire chase.

http://guide.rockwool.co.uk/products/building-insulation/fire-barrier-systems.aspx

It also is directly applied to the Chimney with no airspace

Should pass code in your area double check 

Rock wool does pass the NFPA code ( National Fire Protection Agency..)


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## Bob Mariani (Dec 1, 2008)

21boat said:


> In my neck of the woods we use Rock Wool insulation for fireproofing. Its also required between a chimney when the chinnmey is inside a home penetrates another floor where the box framing around that chimney is a fire chase IE Rock Wool stuffed against the chimney and wood framing stops a fire chase.
> 
> http://guide.rockwool.co.uk/products/building-insulation/fire-barrier-systems.aspx
> 
> ...


this is true, I use it to seal the air leakage at the top plate all the time, but the unit may call for a 2" air space. This area is needed by design and should not be filled with insulation.


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## Gary in WA (Mar 11, 2009)

Yep, I agree with Bob- you need the air space; http://www.rumford.com/code/article.html

The location sounds like it may be only used for a gas flue in the garage, or is it a bedroom fireplace? Did you ask your local AHJ?

Current Code: http://publicecodes.citation.com/icod/irc/2000/icod_irc_2000_10_sec001_par025.htm

Support fire-blocking material, not just stuff-it in: http://publicecodes.citation.com/icod/irc/2000/icod_irc_2000_10_sec001_par026.htm

Gary


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## 21boat (Dec 26, 2008)

GBR in WA said:


> Yep, I agree with Bob- you need the air space; http://www.rumford.com/code/article.html
> 
> The location sounds like it may be only used for a gas flue in the garage, or is it a bedroom fireplace? Did you ask your local AHJ?
> 
> ...


 My posted web site is a NON-combustible material that means the 1” or 2’ to a ‘Combustible is not an issue any more. I am a mason and let me say Chimney block is NOT a “Unit” and those Chimney block can also have insulation in them and are manufactured as such. Also the Rock Wool I suggested is used for a FIRE barrier and we used a ton of that in a Hospital I worked on for soundproofing and Fire stopping. It’s a NON-combustible.

To have an air space is a trade off . For fire to exist you need 3 things Heat, Fuel. Oxygen, A 1” or 2” can also become a fire chase. But the powers to be decided that trade off was acceptable. BUT. Cant transfer fire through a NON Combustible.. 

Many times I deal with Fire chases. Example a PVC pipe going through a floor in a multi dwelling is considered a fire chase. Metal/iron pipe has to be used along with fire proof caulking around that penetration..


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