Chimney clearance for cellulose

cmct1181

1940s cape with brick chimney.  Clay liner was in bad shape so an uninsulated SS liner was installed. Oil boiler. Cellulose insulation in attic in contact with chimney. Does the liner make it zero clearance or does the cellulose need to be moved?

Jamie Hall

The liner does not make it zero clearance. Check your local code -- fire marshal ("asking for a friend" is always good for a laugh) but at least two inches clear.

ethicalpaul

Wow, code really calls for that?

A brick chimney can get hot enough to ignite fire-resistance cellulose at zero inches but is totally fine as long as the cellulose is 2 inches away???

mattmia2

it has more to do with keeping a chimney fire or other malfunction from turning in to a structure fire than getting hot enough to ignite insulation or framing under normal conditions.

cmct1181

So if we were to leave it, besides the risk of a chimney fire, does the brick chimney under normal circumstances ever get hot enough to cause combustion? Cellulose says nothing over 194 degrees. 

mattmia2

You should put a baffle in and move it away. Equipment malfunctioning could do it too.

JUGHNE

I have seen a double or triple? walled wood burner chimney pipe get hot enough to ignite the cellulose
insulation over time.

The heat will eventually lower the ignition point of cellulose (treated paper) or even wood.

Often fiberglass insulation is installed around the chimney or recessed lights (which are a real hazard in themselves). But this is what is sometimes done.....not entirely correct....but better than cellulose.

A plumber left his work light lying in cellulose and it started smoldering within about 30 minutes.

ethicalpaul

But was the work light surrounded by bricks??

JUGHNE

I see your point, but it was surrounded by cellulose.

I was just reporting observations.....cellulose is fire retardant treated paper.....not fireproof.

But brick, old clay liner and SS liner inside, I would not hesitate to wrap the brick with fiberglass.

kcopp

Rock wool.... cant burn.

mattmia2

kcopp said:

Rock wool.... cant burn.

Does house insulation grade rockwool have a binder like fiberglass?

kcopp

https://www.rockwool.com/north-america/products-and-applications/products/safensound/

Bob Harper

A chimney must be suitable for the class of service. All chimneys must be lined. If you perform a level II inspection and determine a flue can no longer perform its intended function, it must be relined, rebuilt or replaced with a listed venting system. All chimney liners are listed to UL 1777. This calls for a nominal 4" wythe wall made of "solid masonry units" surrounding the flue and separating multiple flues. A "solid masonry unit is defined as one having 75% or more of its cross-sectional area solid. A 10 hole cored brick fails. An ungrouted CMU block >4" fail. Now, if the level II has determined the wythe walls are intact including mortar joints at least 75% of their thickness and not softened, crumbling or modified into sand and salt by acids, then that flue can be relined with a listed liner. For CAT I gas and oil, liners do not require insulation. If you seal the top and bottom, it becomes a Dewars flask (Thermos bottle) and minimize condensation. When installed in accordance with its listing, you CAN allow combustibles at zero clearance to the outside face of the chimney. In fact, 99.99% of all chimneys in America are at a zero clearance to combustibles and therefore should be relined with listed liners just for clearances. Cellulosic insulation is considered a 'combustible' material because it cannot pass ASTM E-136. You CAN allow cellulosic insulation against a masonry chimney only once it has been relined with a listed liner. Otherwise, that chimney must meet the code including a 2" clearance to combustibles for interior chimneys/ 1" for exterior chimneys plus firestopping at each ceiling, etc. per the code. Note that while the IRC details how to build a masonry fireplace and chimney, a chimney must meet NFPA 211.
I hope this clarifies things.

cmct1181

Thanks everyone. Because we can’t be sure of the condition of the chimney joints, we’re going to be on the safe side and move it away and put Rockwool around. Thanks again for everyone’s help.