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Posted by Kenneth on March 23, 2008, 7:19 am
On Sun, 23 Mar 2008 03:30:18 -0700 (PDT), tedinoue@gmail.com
wrote:
>> On Sat, 22 Mar 2008 06:09:40 -0700 (PDT), tedin...@gmail.com
>> wrote:
>>
>>
>>
>> >I agree with the comments about not foaming over the ductwork. If you
>> >ever have to do electrical or other work up there, you'll be cursing
>> >yourself.
>>
>> Howdy,
>>
>> Can you please say more about this aspect of your
>> interesting comments?
>>
>> When you use the term "up there" I don't know what you mean.
>>
>> We have under consideration foaming the sides and top of the
>> ducts that run along the floor of an attic space.
>>
>> How might that become a hassle if we were to "do electrical
>> or other work up there" in the future? I ask because the
>> rest of that attic space would be untouched.
>>
>> Sincere thanks,
>> --
>> Kenneth
>
>Up there, meaning the attic.
>
>I think the problem that many of have with this idea is we imagine the
>entire attic floor foamed, with the ducts encapsulated in the foam.
>Reading your note above leads me to think you're just looking at
>foaming the ducts themselves but leaving the rest of the attic floor
>unfoamed. That's probably far less problematic, as it will just put a
>hard shell around the ducts, which should actually protect them in the
>future.
>
>As noted in my original response, the far better solution is to seal
>up the attic, as that has positive effects for the entire house
>envelope. If your air handler is in the attic with the ducts, it also
>greatly reduces the wear and tear on the unit because it makes the
>attic space much closer to inside temperature rather than the 100+F
>that it would be if you use conventional attic venting. Sealing the
>attic also helps to negate the effects of the inevitable leaks in the
>air handler/ducts, increasing the performance of the system. For
>example, in the normal situation, if you have 50 CFM of return air
>leaks outside the conditioned envelope of the house, in your climate,
>that might mean sucking 0F air into the system, resulting in ~12% of a
>4-ton system's capacity wasted. Bring the attic into the conditioned
>envelope and now instead of sucking 0F air, you're sucking maybe 60F
>air into the system and the loss drops to <5%.
>
>-tdi
Hello again,
Thanks for clarifying...
As I believe I described, we have no thought about foaming
over the floor to include the ducts. The plan under
consideration was to do only the ducts themselves.
The idea about increasing the envelope of the house to
include the entire attic makes fine sense, but...
The point of payback seems to be extremely far off (and that
is not based upon your comments alone.)
The cost for doing just the ducts is on the order of $3500,
but the cost of doing the entire attic is on the order of
$12000.
So, based on my calculations, it may be prohibitive.
One of the bids we have suggested removing the glass we how
have on the ducts, and putting it in the roof (instead of
disposing of it) then, foaming the ducts, and adding glass
to the roof where needed. (Also, it would eliminate the
concern about shingles overheating in the sun when foam is
on the other side of the sheathing, though, I don't have any
knowledge of the validity of that concern.)
That might give me (some of) the best of both.
Thanks again,
--
Kenneth
If you email... Please remove the "SPAMLESS."
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