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Old 03-03-2014, 02:47 PM   #1
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Attic Ductwork Insulation


Hello,

I am in Chicago and the builder installed our 2nd HVAC unit in the attic (within an insulated room) but all of my ductwork is in unconditioned attic space. They are flexible tubing with R-8 insulation jacket. A few questions:

1. I am told not to put more insulation (batt or blown in) on top of these insulated ductwork due to condensation. Does this apply to me living in north? Some of my ductwork is buried under blown in insulation...

2. What other ways are there to keep these ducts well insulated other than taking off existing insulation jacket and spray foam?

3. How do you look for leaks in the ductwork in the attic other than with infrared camera or thermometer? Is there some other professional test that can identify leaks?

Thanks

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Old 03-03-2014, 03:07 PM   #2
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Attic Ductwork Insulation


There's no reason the duct work can not be covered with blown in insulation.
Have you air sealed all the places where wiring, plumbing, ceiling fixtures where run though all the top plates and ceilings?
Added baffles to make sure the soffit vents do not get blocked up when adding insulation?
Was foil, not duct tape used on the flex lines?

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Old 03-03-2014, 04:46 PM   #3
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Attic Ductwork Insulation


Joe - yes, to my knowledge they have been but planning to double check air sealing throughout. They used foil but I am planning to use infrared temp tool to at least identify areas where there could be leakage.

Thanks!
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Old 03-03-2014, 04:49 PM   #4
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Attic Ductwork Insulation


"By putting insulation outside the wrap on the first layer of duct insulation, that first wrap will be at a lower temperature. If attic air leaks in, it could condense on the 1st wrap, which is (or should be) a Class I vapor retarder. For that reason, I'd recommend NOT adding insulation unless you also remove the first insulation jacket. Since they don't have Class I vapor retarders, that's also why you wouldn't wrap ducts in wall batts."

From another forum:
http://www.greenbuildingadvisor.com/...ing-hvac-ducts
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Old 03-03-2014, 05:37 PM   #5
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Attic Ductwork Insulation


Quote:
Originally Posted by joecaption View Post
Have you air sealed all the places where wiring, plumbing, ceiling fixtures where run though all the top plates and ceilings?
Added baffles to make sure the soffit vents do not get blocked up when adding insulation?
Well now is a hell of ah poor time to be attempting that. Why wasn't it done when the house was built? Maybe we need more codes.
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Old 03-03-2014, 11:24 PM   #6
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Attic Ductwork Insulation


Well, that link wasn't very helpful as they just said "New Jersey" where cooling days vary from 550-1200 http://climate.rutgers.edu/stateclim...onthly/cdd.htm and Chicago also varies around 850 http://www.sws.uiuc.edu/atmos/statec...-narrative.htm Only for a few months...

It is a big problem in the south, though; http://www.airconceptsllc.com/ac-duct-sweating.html

And HVAC /ducts should not be in any attic, unless conditioned; http://www.buildingscience.com/docum...cold%20climate

How much insulation is installed on the ducts and a HVAC member can figure the dew-points for you (as stated in chart in my south link)... may need to post it again in "HVAC".

Gary
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Old 03-04-2014, 07:40 AM   #7
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Attic Ductwork Insulation


Hi Gary,

Thanks for the info. It sounds like throwing on more insulation or perhaps burying under blown in may not be a bad idea in my area..
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Old 03-04-2014, 09:52 PM   #8
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Attic Ductwork Insulation


IMO, no, I don't see your local climate having a problem. The more insulation above the vapor barrier, the colder it will run. Keep in mind, the loose-fill will slow/catch most of the moisture in the warm attic air- before it get to the R-8 cover and that wrap of insulation under cover is stopping most of the cold anyway- 90%;http://www.google.com/url?sa=t&rct=j...d.cGE&cad=rja; that is the little left from not rising up and out your high exhaust vents. Reading these links, remember cold air has a lot less moisture than warm air and they do split once in the attic; Is my attic insulation adequate?
So you MAY have a little condensation, the 10% loss of R-8 and the little moisture in colder air and only for a couple months of the year, and even less reading of your temperate climate from the lakes...


Gary

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Last edited by Gary in WA; 03-04-2014 at 09:56 PM.
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