Recently I had a home energy audit done. The auditor said there was
bit of air leakage where the furnace stack (a round sheet metal
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
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.
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.
Thanks for all the replies. I did make my way up there and yes, the
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:
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.
I told you what to buy last week. No, you won't find it at home stores, I
told you to go to a plumbing supply house It is used on steam pipe, and
boiler breeching all the time. It can take something like 2200 degrees.
Don't use expandable foam on a flue pipe, it is a fire hazard. Most
rigid fiberglass pipe insulation is good for 800 degrees F. (according
to the data sheets the last time I bought some). There is other pipe
insulation that can go higher in temperature, but why pay for that?
Typically your flue gas temperature will not be over about 300 degrees
F. It depends on how much heat is extracted in the furnace and how
much house air is mixed in at the draft diverter if the furnace has
one. Using sheet metal to block the gap between the flue pipe and the
nearest wood will help block air moving from the house into the attic.
You could also install "B" vent for a gas appliance. It typically does
not need clearance between the flue and adjacent combustible materials.
The B-vent in insulated flue pipe.
THANKS TO ALL! EXCELLENT INFORMATION! FYI - I've checked the ceiling
around the furnace as best I could - not much I could get to
there. I plan to
go into the attic and will NOT be using expandable
foam. I do plan to wrap /
insulate the stack to cut down on the heat
it's giving off. I will also check
the draft area up there to see if I
can seal it off with a metal collar. .
Thanks again for all the ideas!
> Don't use expandable foam on a flue pipe, it is a fire hazard.
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