# Air gap between chimney and house framing



## That Guy (Aug 19, 2017)

I have a chimney that is used by 2 working fireplaces, and the furnace. its in the middle of my house.

In the attic, there is a 3" air gap the apears to go all the way down to stone face on the front hte fire place in the living room.

Should I fill this gap with insulation or leave it be?

Getting a picture will be quite difficult as I just sprayed 18" of loose cellulose up there today.


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## jlhaslip (Dec 31, 2009)

Describe the configuration of the furnace and the surrounding materials, please.

Is the Chimney pipe insulated? Are the walls framed or brick?
Three flues or a single one?


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## That Guy (Aug 19, 2017)

In the attic, it appears the entire chimney is made out of cinder block, then in the basement and living room has stone faced. In the garage, opposit of the living room, its brick. and outside on the room its brick.

3 flues, all 3 are clay.

In the attic, its framed around the chimney with wood framing, creating that gap. 

This past summer, I fillied in on the back of the chimney as far down as I could reach with expanding foam as you could see the light from the garage poking through. 

Also, while in the attic, looking up along the chimney you can see daylight in spots, but there is zero indication of any water coming in.

Going back to my college days, i know the chimney is its own free standing structure, seprate from the house. 

But should I fill that gap the gap created by the framing around the chimney in the attic, or just not worry about it?

I am curious if this is a potential area for loss of heat in the winter.


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## jlhaslip (Dec 31, 2009)

Unless that foam is fire rated (and there is such a foam) it needs to remain separate from the flue by a certain distance, which is dictated by your local/state codes. 
I would find out what that spacing requirement is for your area and adhere to it. 
Maybe block the daylight and leaks using metal?


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## XSleeper (Sep 23, 2007)

If the chimney is double walled (flue inside the block structure) then the framing should be fire blocked tight to the CMU using fire rated materials... usually at the top plate/ceiling, more often if the distance between plates or between floors exceeds 10'.


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