# Can I use ductwork insulation to keep cellulose off attic pipes/vents?



## joecaption (Nov 30, 2011)

Not sure where you got that info.
Insulation around duct work, and soil pipe vents will do no harm.
If there's big holes around the pipes where they just made the holes to big they should be sealed with expanding foam insulation, in fact before you start blowing it's good policy to seal up any holes in the ceiling before the insulating. If you can see light coming from below such as a round a light fixture or ceiling fan seal it up or there's still going to be an air leak.


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## darlingm (Aug 20, 2011)

joecaption said:


> Not sure where you got that info.
> Insulation around duct work, and soil pipe vents will do no harm.
> If there's big holes around the pipes where they just made the holes to big they should be sealed with expanding foam insulation, in fact before you start blowing it's good policy to seal up any holes in the ceiling before the insulating. If you can see light coming from below such as a round a light fixture or ceiling fan seal it up or there's still going to be an air leak.


You know, I'm not sure why I was saying and other pipes too. Guess I've just had too much on my mind, and I'm exhausted. 

As far as the under microwave range exhaust goes, however, I've seen many guides say that you have to keep the insulation from touching it. Below is a page from one of the guides that I've seen say this, although I've seen it in others.

I haven't done this before, and certainly can't speak myself as to whether it's necessary.

buildingscience.com Guide to Attic Air Sealing, pg 38:


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## joecaption (Nov 30, 2011)

That's for a pipe for a vent for a gas fireplace or hot water heater.
Any pipe that does not prduce heat can be insulated right up againt it.
Sewer vents, range hood vents, main power pole that goes through the roof, can be insulated direct contact.
If it's PVC or cast iron, steel pipe it's safe.


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## darlingm (Aug 20, 2011)

joecaption said:


> That's for a pipe for a vent for a gas fireplace or hot water heater.
> Any pipe that does not prduce heat can be insulated right up againt it.
> Sewer vents, range hood vents, main power pole that goes through the roof, can be insulated direct contact.
> If it's PVC or cast iron, steel pipe it's safe.


Ahh, OK, thanks! I figured the range hood vent would be in the same category, figuring it could get pretty hot sometime. Thanks again!


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## Gary in WA (Mar 11, 2009)

It probably wouldn't get hot enough to catch insulation on fire, but I would wrap it with some better R-value than 6 (Code minimum, like a "D" in school) for your location. Picture warm moist air (grease from cooking or boiling water) going through a cold (attic temperature) pipe to condense on the inside walls as it streams past. Foil tape or mastic the seams when going through unconditioned spaces (attics) as the BSC article said. Much better to fully insulate (as if it was a wall) the pipe for your location, then to just add the cellulose around it. The pipe insulation will help stop the convection to the roof-top termination hood connected to the pipe in the attic, as well.

Gary


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