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Best way to close off an old furnace chimney in cold climates?

Kevin_Edmund's picture


We will be installing a new furnace in a new location in an older home ('60's).  The old chimney stack is located in a small bump out, about 1'x1'. We are considering sealing the chimney stack at the bottom and leaving the top of the stack open (as-is). The chimney cap at the top is clay and I assume the stack is clay, but haven't checked yet.

The house and the bump out will stay clad in bricks - so taking out the bump out isn't an option for us.

Any thoughts on the subject?

Are there any breathable caps for old chimneys to keep out the critters and the water/snow, but allow moisture to escape? If so,  would you do both?

Looking forward to your input!



Definitely you want some sort (post #216449, reply #1 of 2)

Definitely you want some sort of cap on top to keep out critters and leaves.  On our working fireplace flue I used a piece of hardware cloth (very coarse screen) bent into a cap and secured with a (very) long spiral hose clamp. 

For a flue you won't be using you can use just about anything.  You could seal it tightly on top (eg, bend up a sheet metal cap) and leave the bottom end open.  I see no need to have it "breatheable" on the top end.

(But note that if this flue is in a common chase with other flues then you may have to protect against leaks between flues.)

Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville

Squirt foam in the bottom and (post #216449, reply #2 of 2)

Squirt foam in the bottom and top to seal against air movement then install a galvanized cap on top to keep out rain and weather.

Florida Licensed Building Contractor, 50 years experience in commercial remodeling, new homes, home remodeling and repairs and all types building maintenance.