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Old 05-27-2014, 08:08 PM   #1
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Will enough cellulose in the attic effectively seal leaky ducts?


I am planning an attic insulation project and am thinking I'l pile up cellulose to get the whole attic to R-50 or so (being careful not to overload the capacity of the drywall, of course). Right now the furnace ductwork is in the unconditioned attic and is barely insulated at all. The flex ducts have like R-4, and the sheet metal trunk duct is just completely exposed with no insulation at all(!). The ceiling already has around 6" thick fiberglass batts between the 2x6 bottom chords with inconsistent and ineffective amounts of cellulose on top. The duct layout is not bad.

There's no mastic or anything nice like that, so I would like to air-seal the ductwork even though I don't anticipate using the furnace much (after all the energy projects, I should be able to get by with a medium sized ductless mini-split heat pump/AC). However, if I pile on 12"+ of cellulose over the ducts, is there any chance that after it settles, that will be a decent enough air barrier? Or should I just bite the bullet and mastic the hell out of the ducts or encapsulate them in spray foam before spraying the cellulose?

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Old 05-27-2014, 09:15 PM   #2
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Will enough cellulose in the attic effectively seal leaky ducts?


You need to seal all openings on the duct work. Otherwise it is going to pull in dust and/or insulation into the system.

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Old 05-27-2014, 09:25 PM   #3
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Will enough cellulose in the attic effectively seal leaky ducts?


+1. Any loose fill insulation will not effectively seal the ducts. Mastic at the joints+ the insulation blown over would be the most cost effective solution.
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Old 05-27-2014, 11:29 PM   #4
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Will enough cellulose in the attic effectively seal leaky ducts?


Ugh, I was hoping you wouldn't say that… The attic is super cramped and scary to work in. Guess I'll just have to figure out a way.
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Old 05-28-2014, 05:34 AM   #5
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Will enough cellulose in the attic effectively seal leaky ducts?


Yep, seal the ducts.
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Old 05-28-2014, 09:00 AM   #6
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Will enough cellulose in the attic effectively seal leaky ducts?


Quote:
Originally Posted by iLikeDirt View Post
Ugh, I was hoping you wouldn't say thatÖ The attic is super cramped and scary to work in. Guess I'll just have to figure out a way.
Best bet, pay someone else to suffer the job. Cramped spaces, heat, and the like, ugh. Make sure when you're up there someone else is in the house and keeping tabs on you. It'd be a shame to die from heat exhaustion trapped in your own attic, just to avoid paying someone else to do the job...
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Old 05-28-2014, 09:26 PM   #7
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Will enough cellulose in the attic effectively seal leaky ducts?


+1

Seal them first.

Nothing about loose fill seals them.
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Old 05-28-2014, 11:00 PM   #8
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Will enough cellulose in the attic effectively seal leaky ducts?


http://www.thisoldhouse.com/toh/vide...506126,00.html

Check out this link for an interesting way to seal ducts from the inside.
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Old 05-29-2014, 12:02 AM   #9
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Will enough cellulose in the attic effectively seal leaky ducts?


Energy auditors are funny. All that smoke to tell you what you could see with the naked eye. They just like to party.
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Old 05-31-2014, 12:07 AM   #10
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Will enough cellulose in the attic effectively seal leaky ducts?


Oops. The link I had in my previous post was incorrect. Here is the right one.

http://www.thisoldhouse.com/toh/tv/a...797676,00.html

Click on "scene 4" to get to the part about duct sealing.
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Old 06-01-2014, 12:55 PM   #11
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Will enough cellulose in the attic effectively seal leaky ducts?


Quote:
Originally Posted by Dave Sal View Post
Oops. The link I had in my previous post was incorrect. Here is the right one.

http://www.thisoldhouse.com/toh/tv/a...797676,00.html

Click on "scene 4" to get to the part about duct sealing.
Google AeroSeal for an easier selection of videos.

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