Insulate and seal a furnace stack in the attic?

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!
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damncold

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damncold wrote:

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
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Speedy Jim wrote:

You are too speedy, he is talking about loss from the living space.
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George E. Cawthon wrote:

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
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Speedy Jim wrote:

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.
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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:

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damncold

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damncold 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.
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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.
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Ed
http://pages.cthome.net/edhome/



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Edwin Pawlowski wrote:

That's good but at 2200 degrees his stack probably won't be there to support the fiberglass.
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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.
Stretch
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THANKS TO ALL! EXCELLENT INFORMATION! FYI - I've checked the ceiling area 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!
Stretch Wrote: > Don't use expandable foam on a flue pipe, it is a fire hazard. Most

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damncold

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I'd use fiberglass.

Thee is fiberglass insulation made for pipes and stacks. Check with a plumbing supply house. Comes in about 3' lengths and is curved to fit pipes.
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