# Will enough cellulose in the attic effectively seal leaky ducts?



## iLikeDirt (Apr 27, 2014)

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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## gregzoll (Dec 25, 2006)

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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## HomeSealed (Jan 3, 2008)

+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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## iLikeDirt (Apr 27, 2014)

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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## beenthere (Oct 11, 2008)

Yep, seal the ducts.


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## wkearney99 (Apr 8, 2009)

iLikeDirt said:


> 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.


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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## Windows on Wash (Aug 30, 2011)

+1

Seal them first.

Nothing about loose fill seals them.


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## Dave Sal (Dec 20, 2012)

http://www.thisoldhouse.com/toh/video/0,,20506126,00.html

Check out this link for an interesting way to seal ducts from the inside.


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## Windows on Wash (Aug 30, 2011)

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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## Dave Sal (Dec 20, 2012)

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

http://www.thisoldhouse.com/toh/tv/ask-toh/video/0,,20797676,00.html

Click on "scene 4" to get to the part about duct sealing.


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## Windows on Wash (Aug 30, 2011)

Dave Sal said:


> Oops. The link I had in my previous post was incorrect. Here is the right one.
> 
> http://www.thisoldhouse.com/toh/tv/ask-toh/video/0,,20797676,00.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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