damncold wrote:
Thanks for all the replies. I did make my way up there and yes, the
area around the stack is warm and the snow on the roof above it is
melted. I could not see well enough to determine how much space there
was around the stack. I would like to stop the stack itself from
heating the attic. I've checked at some home stores but no one seems
really confident if you can put insulation around a stack or not. And
if you could, what kind. Any ideas?


George E. Cawthon Wrote:

Speedy Jim wrote:
George E. Cawthon wrote:

Speedy Jim wrote:

damncold wrote:

Recently I had a home energy audit done. The auditor said there was
quite a bit of air leakage where the furnace stack (a round sheet
metal
stack) comes into the attic. He said I should seal the by-pass in
the
attic and "thought" expandable foam would be OK. Anyone know if this
could be a fire hazard?
He also pointed out that the furnace stack is not insulated and is
giving off a good deal of heat in the attic - which is evident by the
size of the icicles hanging from my eaves. Is there any safe way to
insulate a metal furnace stack? Keep in mind - this is a crawl-space
sized attic. I've been up there before and it is very hard to move
around in. Thanks!



Insulating the flue pipe in the attic will have almost ZERO effect
on your energy consumption. Any heat now being lost up there is
being transferred to the roof or whisked out the gable/soffit vents.

Sealing around it to stop air movement from the living space will
be beneficial.

Jim


You are too speedy, he is talking about loss from the living space.



No. There were *two* separate issues. Here is the second one, as
presented by OP:

"He also pointed out that the furnace stack is not insulated and is
giving off a good deal of heat in the attic "

It being hard to work in the limited crawl space he has,
insulating this sounded like a losing proposition.
Jim

Ok, I missed that. There is a point in insulating
it. If the attic remains cold he is less likely
to have ice dams form. I'll bet that most of the
heat he see in the attic is from the hole (around
the stack) between the living area and the attic.
So in essence, I agree with you, insulating the
stack in the attic is rather a waste.




I suggest that you use fiberglass to seal around
the stack where it comes from the living space
into the attic first. ( BTW, you also can stop air
movement by putting a metal collar around the
stack; screw the collar to the ceiling (or the
floor of the attic and use fire caulk between the
collar and the pipe. this is a pretty standard
practice for gas furnace stacks here.)
Then see if there is much heat in the attic. If
you still want to insulate the stack in the attic
then just wrap with a 2-4" blanket of fiberglass
held in place with wire ties. Most stacks can be
as close as 2-3" from wood surfaces, so the
temperature must be well below damaging
fiberglass. If you are worried about doing that
(fiberglass bursting into flame or transmitting
the heat to something nearby) then you better
doubly worry about the wood frame penetrated by
the stack in the present condition.