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Posted by Stormin Mormon on March 21, 2008, 8:38 am
Fiberglass with vapor barrier?
--
Christopher A. Young
Learn more about Jesus
www.lds.org
Given the temperature delta (80 or so in the ducts, and
occasionally 0 in the unconditioned surroundings) the glass
does a very poor job because of losses to convection.
All the best,
--
Kenneth
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Posted by Kenneth on March 21, 2008, 10:37 am
On Fri, 21 Mar 2008 06:54:54 -0500, Don Ocean
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>> Given the temperature delta (80 or so in the ducts, and
>> occasionally 0 in the unconditioned surroundings) the glass
>> does a very poor job because of losses to convection.
>What????
Hi again,
I am not sure what you are asking, but...
It is my understanding (and I am only repeating what I have
been told) that if there are very significant temperature
differentials, and the fiberglass is not completely boxed
in, or otherwise, sealed, its R value will drop
significantly due to convection.
Few know less than I about HVAC, but I do know a bit about
physics, and that makes sense to me. Certainly, if I were to
blow a hair dryer into a foot of fiberglass I could feel the
warm air coming though the other side.
I would be happy to understand more,
--
Kenneth
If you email... Please remove the "SPAMLESS."
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Posted by KAubert (Air-Care) on March 21, 2008, 10:46 am
Hi all:
We are seeing more of the foam insulation here on the coast. I have
not seen anyone try to foam over the ducts.
I will say this; I have seen where loose fill was applied completely
over ducts and made very nice stain tracks on the ceiling. I can see
where condensation could be a problem with foam covered ducts;
especially if open cell foam were used.
Keith
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> Howdy,
> We have a geo water to air system with ducts running through
> an unconditioned attic.
> The ducts are not sealed, but they are (very modestly)
> insulated with a shiny, "quilted" looking product.
> We are soon to foam over them, but...
> There are two different approaches in the bids we have:
> One wants to remove the quilted stuff, and then foam over
> the bare metal of the ducts.
> The other wants to foam over the existing insulating
> material.
> What would you suggest in this regard, and why?
> Sincere thanks,
> --
> Kenneth
> If you email... Please remove the "SPAMLESS."
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Posted by Kenneth on March 21, 2008, 10:59 am
On Fri, 21 Mar 2008 07:46:34 -0700 (PDT), "KAubert
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>I will say this; I have seen where loose fill was applied completely
>over ducts and made very nice stain tracks on the ceiling. I can see
>where condensation could be a problem with foam covered ducts;
>especially if open cell foam were used.
>Keith
Hi Keith,
Can you say something more about why the (potential)
condensation problem would be greater with open cell?
Thanks,
--
Kenneth
If you email... Please remove the "SPAMLESS."
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Posted by Kenneth on March 21, 2008, 11:28 am
On Fri, 21 Mar 2008 10:59:03 -0400, Kenneth
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>On Fri, 21 Mar 2008 07:46:34 -0700 (PDT), "KAubert
>>I will say this; I have seen where loose fill was applied completely
>>over ducts and made very nice stain tracks on the ceiling. I can see
>>where condensation could be a problem with foam covered ducts;
>>especially if open cell foam were used.
>>Keith
>Hi Keith,
>Can you say something more about why the (potential)
>condensation problem would be greater with open cell?
>Thanks,
Hi Again Keith,
I have continued to think about your comments above, and
realize that we have no condensation problem whatever
despite having fiberglass simply laid over the ducts.
We use lots of AC for several months of the year, but I have
never noticed so much as a drip.
All the best,
--
Kenneth
If you email... Please remove the "SPAMLESS."
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>> occasionally 0 in the unconditioned surroundings) the glass
>> does a very poor job because of losses to convection.
>What????