How to block gap around chimney at attic floor?

[John]

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.

[hallerb]

gap is there to prevent chimey from overheating and causing fire.

if I understand your post dont block it.

some air leaks are intentional

[RicodJour]

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.

R

[RicodJour]

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.

R

[siralfred]

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

[Kathy]

and stuff the gap with

would that pass inspection?

[CBHVAC]

Doubt it...

[siralfred]

I saw it in a Time/Life how-to book about weatherproofing and insulation. Published in 1977. Doesn't say if it's code or not, but I doubt they would print it without checking.

[unsquishables]

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[hallerb]

hey a reply to a disscusion from 2006:) google groups must of had a tech problem

[mm]

That sounds good. See further down.

I don't know what the preferred method is but this week at Home Depot in the paint departament caulking section I came across 3M Fire Barrier and 3M Fire Block. You can read about them online. I am not sure which is which. One or both are meant for filling around pipes that run through the floor, etc. I doubt the outside of your chimney gets anywhere near too hot for these products, but others may have their say.

[mm]

Dang!