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Old 05-20-2014, 04:05 PM   #1
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best way to insulate this metal duct



I was expecting to find some sort of ductwork in this wall and this is what it looks like. I was considering buying one of those small (100 bf) spray foam kits to fill in voids that I can't reach with Roxul. Would coating this duct in foam be worth doing, or is there a better way?

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Old 05-20-2014, 04:35 PM   #2
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Do you know fore sure it isn't insulated internally?

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Old 05-20-2014, 05:16 PM   #3
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Well, I never thought about that. This house was built in 1979 and as far as I can tell, the house was build with forced air, so I'd wager this duct is original. I had just assumed due to the age that it wasn't.
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Old 05-21-2014, 11:01 AM   #4
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best way to insulate this metal duct


Why do you want to insulate it?

Looks like a mechanical chase and a duct run. If it is between conditioned spaces, there is not need to insulate it as long as you separate the barrier between conditioned and unconditioned spaces and place your insulation layer there.

If it is exposed on the attic side, seal it off at the attic floor and insulate over the top.
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Old 05-21-2014, 10:49 PM   #5
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If it is between conditioned spaces, there is not need to insulate it as long as you separate the barrier between conditioned and unconditioned spaces and place your insulation layer there.
Could you restate that in a way I could follow?

This is the supply trunk for the second floor. The air handler is in the basement and this duct runs up into the attic. These pictures are of the first floor. The space is bordered on two sides by the foyer, one side by a half bath, and the other an exterior wall. The exterior wall consists of brick followed by 1 in of xps followed by 3.5 in of Roxul (when I'm done). While I have this space open on 3 of 4 sides I'm air sealing and reinsulating and now's the time to deal with this duct, if it needs it.

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If it is exposed on the attic side, seal it off at the attic floor and insulate over the top.
That's on the list too.
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Old 05-22-2014, 11:01 AM   #6
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best way to insulate this metal duct


The exterior wall is your envelope wall in this case.

Make sure that wall between the brick and the chase is well insulated and sealed. Other than that, communication with the interior walls is fine and does not require insulation or air sealing.
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Old 05-22-2014, 05:51 PM   #7
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Keep in mind that minimum code requires air sealing against fire between floors/ceilings (first/second) including in a chase (enclosed space); http://publicecodes.cyberregs.com/ic...002_par017.htm

Here is a good guide; How to fireblock framing

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Old 05-23-2014, 06:20 AM   #8
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Originally Posted by Gary in WA View Post
Keep in mind that minimum code requires air sealing against fire between floors/ceilings (first/second) including in a chase (enclosed space); http://publicecodes.cyberregs.com/ic...002_par017.htm

Here is a good guide; How to fireblock framing

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Good catch Gary. Looks like they might have some in there but now is certainly the time to make sure it is right and add to it if needed.
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Old 05-23-2014, 04:31 PM   #9
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Good catch Gary. Looks like they might have some in there but now is certainly the time to make sure it is right and add to it if needed.
Nope, nothing. Unless failed crumbly UFFI counts, which I doubt. So I need to seal the small gaps around the duct and pipes with fire foam. In the joist space between the first and second floors I'll need to seal that up too. Hmm... another can of worms opened.
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Old 05-24-2014, 06:13 PM   #10
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Yep, it didn't look like it was even attempted between floors, I see that all the time...

Use an approved solid material over/under the framing of the plumbing chase, if using fiberglass; it requires 16" thick; http://publicecodes.cyberregs.com/ic...002_par018.htm

Should have mentioned to go two "next section" forward to read the particulars; http://publicecodes.cyberregs.com/ic...002_par019.htm don't forget to foam the wiring holes, also.

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