How to block gap around chimney at attic floor?

Posted by John on January 1, 2006, 10:34 am

I've got a 200 year old center chimney cape, that has a warm attic space.
Mostly, it appears that warm air is rising into the attic through a 2 inch
gap between the floor and the brick chimney. Previous owners had a few
wooden shingles and some fiberglass insulation there as an attempt to block
it. We've got the venting pretty well covered, but a surprising amount of
warm air is coming through that gap!
What is the preferred way to block this gap? I'm thinking of getting some
sheet metal to cover the gap ( as found with a google search ). The chimney
is lined with a clay liner and one flue is used to vent the furnace but I'm
thinking the biggest concern would be when we light the fireplace a few
times a year.
I'm guessing that this problem is very common, and an effective solution is
well known? Any thing better than sheet metal?
Thanks for any info on this.
-Johny B.

Posted by hallerb on January 1, 2006, 11:05 am

gap is there to prevent chimey from overheating and causing fire.
if I understand your post dont block it.
some air leaks are intentional

Posted by RicodJour on January 1, 2006, 11:13 am

hall...@aol.com wrote:
show/hide quoted text
Like where?
That gap between the framing and the brick chimney is to prevent fires,
but the vertical connections between floors should be firestopped at
the floor level to prevent fires from spreading. They're not mutually
exclusive.

Posted by RicodJour on January 1, 2006, 11:05 am

John wrote:
show/hide quoted text
Cutting the sheet metal to fit so tightly that it would cut off the air
flow would be essentially impossible, so you'd have to use a
firestopping caulk. The big box stores sell tubes of the stuff. But
personally, I don't think it's worth the trouble to use metal. Unfaced
fiberglass insulation stuffed into the gap is fine. The paper facing
on insulation burns, so you should take it off.

Posted by siralfred on January 2, 2006, 9:12 am

Wrap the chimney with heavy duty aluminum foil and stuff the gap with
fiberglass insulation without paper.

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