Insulate duct or not to?

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  #1  
Old 12-30-12, 10:01 AM
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Insulate duct or not to?

My attic is within conditioned space (closed cell sprayed foam on roof, no ventilation). When installing my AC ductwork is it still necessary to insulate it? Is there a code that addresses this?

thanks
gary
 
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Old 12-30-12, 10:07 AM
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I doubt a code issue but do you want to lose any cold air to an area you aren't using.
I would bet that even though the attic is fully insulated.......it gets warm in the summer. That heat would be transferred to your A/C ducting.

I know....insulating ducts is a real pain in the *ss but it's definitely worth it.
 
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Old 12-30-12, 10:08 AM
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No reason to insulate in a conditioned space that I can think of. In fact I think you DON'T want to do that. Just seal any joints.

Is it really conditioned? Is there insulation on the ceiling of the spaces below? Slight warming or cooling of the attic space would seem to give you a "buffer zone" to the living space?

Don't think code addresses this...but no expert. Basing what I said on what I've read and seen on home shows.
 
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Old 12-30-12, 11:00 AM
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I consider it conditioned space. There is some unfaced sound insulation between the ceiling and the attic but I do have some vents between the attic and the living space for air exchange.
 
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Old 12-30-12, 11:10 AM
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Since you have air exchange...I can't see that insulating the ducts would be beneficial.
 
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Old 12-30-12, 03:54 PM
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conditioned space

since you say that you have vents from outside to attic, then the attic is not sealed and you must insulate the ducts.if you do not then your ducts will sweat profusely.if the attic is sealed then I would still insulate ducts and i would condition the attic with a small supply and return duct to prevent the dew point temperatures from being reached in the attic space, again causing sweating. Hope this helps.
 
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Old 12-31-12, 06:01 PM
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juddman,

I think you misread zoom's reply about the vents. The vents are not to the outdoors but to the living space. With the attic sealed from the outdoors & ventilation to the living space, the attic would then, IMO, be considered conditioned & one would not want to insulate the ducts.
 
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Old 12-31-12, 08:25 PM
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Grady you are correct, the attic is sealed to the outside, but ventilated to living space below for air exchange.
I originally thought that it would be a waste of time and effort to insulate these ducts but now Im not so sure. I've been researching and was advised that R8 is minimum for unconditioned space and R6 for all other areas according to the IRC. To be honest I don't know what to do now. I will attempt to find out my local code first but if I can't find out, I guess it won't hurt to insulate it. I will just have a small supply up there to condition the air.
 
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Old 12-31-12, 08:40 PM
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Hi zoom,
I haven't read the entire thread, but an isolated attic space, even though insulated to the outside will be somewhat cooler than a fully conditioned space. Condensation would be my concern with warm humid air passing through a cooler duct. In reality, it would be more of an issue when the system wasn't circulating air, with warm air just being pushed to the upper areas. Even those vents you are providing will be carrying moisture into the attic, but unknown if the inside surface will be cold enough to be a problem. If you humidify or have a known high humidity level, then you may want to add supply and return to that space.

There have been some papers on this issue of semi-conditioned attics and I can try to locate if interested.

Bud
 
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Old 01-01-13, 12:59 AM
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It is never wrong to insulate ductwork but sometimes it is not cost effective to insulate over a bare minimum. If I were you I would probably insulate these ducts to around R-4 or maybe R-6 maximum.
 
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Old 01-01-13, 09:37 AM
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The company that I work for will always insulate the ductwork with these conditions.
 
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Old 01-01-13, 02:50 PM
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Thanks for all of your replies. I've decided I will insulate just to be safe. My plan is to supply some small air to the attic space to try and keep it close to the same conditions as the rest of the house. The article at the following link (Ducts in Conditioned Space - ToolBase TechSpecs) from 2006 basically says its not necessary to insulate but it won't kill me and i'd rather be safe then sorry.

thanks again all
Gary
 
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Old 01-01-13, 03:18 PM
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If you put a supply duct into the attic, make sure to also install an equally sized return.
 
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