My attic will be insulated on November 30 of this year. They will
blow in 24" of insulation. I have questions about the existing
ductwork. (Ductwork is 10 and 12 inch flexible insulated ducts)
Presently the ducts are laying within the ceiling joist cavity. When
they blow in the insulation, unless they take special care, it is
likely that the bottom quarters of the round ducts might end up with
little or no insulation. In many cases the ducts are 12" nominal and
fill up (because of the extra large outside diameter) most of the
14-1/2" 2"x6" joist cavity. Ergo, the insulation will not be blown
under the duct. However, there will still be a total of 24" of
insulation, approx. 10" of it covering the entire duct.

Question: Air (when not in motion) is a reasonable insulator so I
should leave things alone. Alternatively, it would take very little
work to simply place slats under the ductwork so they sit above the
ceiling joists, allowing them to fill the entire joist cavity.
Obviously, by raising the ducts six inches, I would be getting less
insulation on top of the ducts.

Does any of this matter? Am I wasting my time thinking about this?
BTW, my contractor is very cooperative and will do whatever I ask. He
will even raise the ductwork upon slats at no charge to me.

Opinions greatly appreciated.

Thank you,

Ivan Vegvary

On 11/22/2010 8:17 PM, Ivan Vegvary wrote:
My attic will be insulated on November 30 of this year. They will
blow in 24" of insulation. I have questions about the existing
ductwork. (Ductwork is 10 and 12 inch flexible insulated ducts)
Presently the ducts are laying within the ceiling joist cavity. When
they blow in the insulation, unless they take special care, it is
likely that the bottom quarters of the round ducts might end up with
little or no insulation. In many cases the ducts are 12" nominal and
fill up (because of the extra large outside diameter) most of the
14-1/2" 2"x6" joist cavity. Ergo, the insulation will not be blown
under the duct. However, there will still be a total of 24" of
insulation, approx. 10" of it covering the entire duct.

Question: Air (when not in motion) is a reasonable insulator so I
should leave things alone. Alternatively, it would take very little
work to simply place slats under the ductwork so they sit above the
ceiling joists, allowing them to fill the entire joist cavity.
Obviously, by raising the ducts six inches, I would be getting less
insulation on top of the ducts.

Does any of this matter? Am I wasting my time thinking about this?
BTW, my contractor is very cooperative and will do whatever I ask. He
will even raise the ductwork upon slats at no charge to me.

Opinions greatly appreciated.

Thank you,

Ivan Vegvary

I'd say you want the ducts as close to the heated envelope as possible,
the better to not be heating the attic. The insulation value of
flexi-duct is close to nil- better than bare metal, but not by much. The
heat they leak should more than make up for any air gap around them.

But I am not an HVAC expert, so what do I know?

--
aem sends...

On Nov 22, 8:17*pm, Ivan Vegvary wrote:
My attic will be insulated on November 30 of this year. *They will
blow in 24" of insulation. *I have questions about the existing
ductwork. *(Ductwork is 10 and 12 inch flexible insulated ducts)
Presently the ducts are laying within the ceiling joist cavity. *When
they blow in the insulation, unless they take special care, it is
likely that the bottom quarters of the round ducts might end up with
little or no insulation. *In many cases the ducts are 12" nominal and
fill up (because of the extra large outside diameter) most of the
14-1/2" 2"x6" joist cavity. *Ergo, the insulation will not be blown
under the duct. *However, there will still be a total of 24" of
insulation, approx. 10" of it covering the entire duct.

Question: *Air (when not in motion) is a reasonable insulator so I
should leave things alone. *Alternatively, it would take very little
work to simply place slats under the ductwork so they sit above the
ceiling joists, allowing them to fill the entire joist cavity.
Obviously, by raising the ducts six inches, I would be getting less
insulation on top of the ducts.

Does any of this matter? *Am I wasting my time thinking about this?
BTW, my contractor is very cooperative and will do whatever I ask. *He
will even raise the ductwork upon slats at no charge to me.

Opinions greatly appreciated.

Thank you,

Ivan Vegvary

You're over thinking this. Imho it will be fine.

On Mon, 22 Nov 2010 17:17:41 -0800 (PST), Ivan Vegvary
wrote:

My attic will be insulated on November 30 of this year. They will
blow in 24" of insulation.

From where? The top?

I have questions about the existing
ductwork. (Ductwork is 10 and 12 inch flexible insulated ducts)
Presently the ducts are laying within the ceiling joist cavity. When
they blow in the insulation, unless they take special care, it is
likely that the bottom quarters of the round ducts might end up with
little or no insulation. In many cases the ducts are 12" nominal and
fill up (because of the extra large outside diameter) most of the
14-1/2" 2"x6" joist cavity. Ergo, the insulation will not be blown
under the duct. However, there will still be a total of 24" of
insulation, approx. 10" of it covering the entire duct.

Question: Air (when not in motion) is a reasonable insulator so I
should leave things alone. Alternatively, it would take very little
work to simply place slats under the ductwork so they sit above the
ceiling joists, allowing them to fill the entire joist cavity.
Obviously, by raising the ducts six inches, I would be getting less
insulation on top of the ducts.

If insulation won't get under any part of the ducts now, why would it
get under the ducts then? Or do you mean that there will be a part
that is 6" high and 10 or 12 inches wide that will get insulation, and
the part just below the round duct won't? Oh, it all will. Then why
do think there will be no insulation undre the duct if you don't raise
the duct? There will be no insulation under the very bottom of the
duct, but that is touching the ceiling downstairs and will warm it a
little.

Does any of this matter? Am I wasting my time thinking about this?
BTW, my contractor is very cooperative and will do whatever I ask. He
will even raise the ductwork upon slats at no charge to me.

Does he have an opinion whether it's a good idea or not? Actually
there's a good chance he doesn't know. This is the kind of obcure
question that rarely comes up, for which there is little empirical
data, less of it in his possession, because after he does his job, he
doesn't stay there all winter to compare this year's figures with last
years.

Opinions greatly appreciated.

I don't think it would help, and might well be bad because of less
insulation abvoe the duct.

Thank you,

Ivan Vegvary

Ivan Vegvary wrote:
My attic will be insulated on November 30 of this year. They will
blow in 24" of insulation. I have questions about the existing
ductwork. (Ductwork is 10 and 12 inch flexible insulated ducts)
Presently the ducts are laying within the ceiling joist cavity. When
they blow in the insulation, unless they take special care, it is
likely that the bottom quarters of the round ducts might end up with
little or no insulation. In many cases the ducts are 12" nominal and
fill up (because of the extra large outside diameter) most of the
14-1/2" 2"x6" joist cavity. Ergo, the insulation will not be blown
under the duct. However, there will still be a total of 24" of
insulation, approx. 10" of it covering the entire duct.

Question: Air (when not in motion) is a reasonable insulator so I
should leave things alone. Alternatively, it would take very little
work to simply place slats under the ductwork so they sit above the
ceiling joists, allowing them to fill the entire joist cavity.
Obviously, by raising the ducts six inches, I would be getting less
insulation on top of the ducts.

Does any of this matter? Am I wasting my time thinking about this?
BTW, my contractor is very cooperative and will do whatever I ask. He
will even raise the ductwork upon slats at no charge to me.

Opinions greatly appreciated.

Thank you,

Ivan Vegvary
One thing to think about...
I learned by accident that insulation is HEAVY.
IN particular, cellulose insulation looks cost effective, but
is heavier than
fiberglass, BUT as it ages, it absorbs moisture and becomes
MUCH heavier. Depending on the construction of your ceiling
and how well it's attached, this may become an issue.
I was planning a DIY cellulose installation. Glad I didn't.

I'd at least ask the question of your contractor.

On Nov 22, 6:23*pm, mm wrote:
On Mon, 22 Nov 2010 17:17:41 -0800 (PST), Ivan Vegvary

wrote:
My attic will be insulated on November 30 of this year. *They will
blow in 24" of insulation.

From where? *The top?

Yes, from above. * * * * * *

If insulation won't get under any part of the ducts now, why would it
get under the ducts then? *Or do you mean that there will be a part
that is 6" high and 10 or 12 inches wide that will get insulation, and
the part just below the round duct won't? *Oh, it all will. *Then why
do think there will be no insulation undre the duct if you don't raise
the duct? *There will be no insulation under the very bottom of the
duct, but that is touching the ceiling downstairs and will warm it a
little.

The 12" ducts take up the whole joist cavity and the sides of the duct
are touching the abutting ceiling joist. Therefore, no blown
insulation will filter down into the two quarter-arcs on either side
of the joint.
However, as somebody else pointed out, the ducts should be closer to
room temperature and not attic (well vented) temperature. This would
argue for the ducts to stay close to the ceiling with lots of
insulation on top even though some will be missing at the lower areas.


Ivan Vegvary

On Nov 22, 6:26*pm, mike wrote:
Ivan Vegvary wrote:
My attic will be insulated on November 30 of this year. *They will
blow in 24" of insulation. *I have questions about the existing
ductwork. *(Ductwork is 10 and 12 inch flexible insulated ducts)
Presently the ducts are laying within the ceiling joist cavity. *When
they blow in the insulation, unless they take special care, it is
likely that the bottom quarters of the round ducts might end up with
little or no insulation. *In many cases the ducts are 12" nominal and
fill up (because of the extra large outside diameter) most of the
14-1/2" 2"x6" joist cavity. *Ergo, the insulation will not be blown
under the duct. *However, there will still be a total of 24" of
insulation, approx. 10" of it covering the entire duct.

Question: *Air (when not in motion) is a reasonable insulator so I
should leave things alone. *Alternatively, it would take very little
work to simply place slats under the ductwork so they sit above the
ceiling joists, allowing them to fill the entire joist cavity.
Obviously, by raising the ducts six inches, I would be getting less
insulation on top of the ducts.

Does any of this matter? *Am I wasting my time thinking about this?
BTW, my contractor is very cooperative and will do whatever I ask. *He
will even raise the ductwork upon slats at no charge to me.

Opinions greatly appreciated.

Thank you,

Ivan Vegvary

One thing to think about...
I learned by accident that insulation is HEAVY.
IN particular, cellulose insulation looks cost effective, but
is heavier than
fiberglass, BUT as it ages, it absorbs moisture and becomes
MUCH heavier. *Depending on the construction of your ceiling
and how well it's attached, this may become an issue.
I was planning a DIY cellulose installation. * Glad I didn't.

I'd at least ask the question of your contractor.

Good point! As it happens, this is an old house with weird
construction. All of the ceilings have 1/2" plywood on the bottom
covered with 3/8" drywall. Structurally very sturdy. While I
certainly try to stand on joists only, I am able to stand on the
ceiling and not break through, even at 230 lbs.

Thanks, Ivan Vegvary

"Ivan Vegvary" wrote in message
...
My attic will be insulated on November 30 of this year. They will
blow in 24" of insulation. I have questions about the existing
ductwork. (Ductwork is 10 and 12 inch flexible insulated ducts)
Presently the ducts are laying within the ceiling joist cavity. When
they blow in the insulation, unless they take special care, it is
likely that the bottom quarters of the round ducts might end up with
little or no insulation. In many cases the ducts are 12" nominal and
fill up (because of the extra large outside diameter) most of the
14-1/2" 2"x6" joist cavity. Ergo, the insulation will not be blown
under the duct. However, there will still be a total of 24" of
insulation, approx. 10" of it covering the entire duct.

Question: Air (when not in motion) is a reasonable insulator so I
should leave things alone. Alternatively, it would take very little
work to simply place slats under the ductwork so they sit above the
ceiling joists, allowing them to fill the entire joist cavity.
Obviously, by raising the ducts six inches, I would be getting less
insulation on top of the ducts.

Does any of this matter? Am I wasting my time thinking about this?
BTW, my contractor is very cooperative and will do whatever I ask. He
will even raise the ductwork upon slats at no charge to me.

Opinions greatly appreciated.

Thank you,

Ivan Vegvary

I wouldn't worry about it. There will be very little airspace there, and if
it is, air is a good insulator with another 12" or more of insulating
material over the top of that. About the only thing you could do is shake
your house really hard to get it to settle that last little bit, but that
would damage a lot. I wouldn't worry about it. With 24", that's about as
good as it gets.

Steve

Heart surgery pending?
Read up and prepare.
Learn how to care for a friend.
http://cabgbypasssurgery.com

On Mon, 22 Nov 2010 19:46:55 -0800 (PST), Ivan Vegvary
wrote:

On Nov 22, 6:23*pm, mm wrote:
On Mon, 22 Nov 2010 17:17:41 -0800 (PST), Ivan Vegvary

wrote:
My attic will be insulated on November 30 of this year. *They will
blow in 24" of insulation.

From where? *The top?

Yes, from above. * * * * * *

If insulation won't get under any part of the ducts now, why would it
get under the ducts then? *Or do you mean that there will be a part
that is 6" high and 10 or 12 inches wide that will get insulation, and
the part just below the round duct won't? *Oh, it all will. *Then why
do think there will be no insulation undre the duct if you don't raise
the duct? *There will be no insulation under the very bottom of the
duct, but that is touching the ceiling downstairs and will warm it a
little.

The 12" ducts take up the whole joist cavity and the sides of the duct
are touching the abutting ceiling joist. Therefore, no blown
insulation will filter down into the two quarter-arcs on either side
of the joint.
However, as somebody else pointed out, the ducts should be closer to
room temperature and not attic (well vented) temperature. This would
argue for the ducts to stay close to the ceiling with lots of
insulation on top even though some will be missing at the lower areas.

How much are they charging you to blow the insulation in. Total
price, insulation and labor and whatever else.


Ivan Vegvary

On Mon, 22 Nov 2010 19:49:27 -0800 (PST), Ivan Vegvary
wrote:

On Nov 22, 6:26*pm, mike wrote:
Ivan Vegvary wrote:
My attic will be insulated on November 30 of this year. *They will
blow in 24" of insulation. *I have questions about the existing
ductwork. *(Ductwork is 10 and 12 inch flexible insulated ducts)
Presently the ducts are laying within the ceiling joist cavity. *When
they blow in the insulation, unless they take special care, it is
likely that the bottom quarters of the round ducts might end up with
little or no insulation. *In many cases the ducts are 12" nominal and
fill up (because of the extra large outside diameter) most of the
14-1/2" 2"x6" joist cavity. *Ergo, the insulation will not be blown
under the duct. *However, there will still be a total of 24" of
insulation, approx. 10" of it covering the entire duct.

Question: *Air (when not in motion) is a reasonable insulator so I
should leave things alone. *Alternatively, it would take very little
work to simply place slats under the ductwork so they sit above the
ceiling joists, allowing them to fill the entire joist cavity.
Obviously, by raising the ducts six inches, I would be getting less
insulation on top of the ducts.

Does any of this matter? *Am I wasting my time thinking about this?
BTW, my contractor is very cooperative and will do whatever I ask. *He
will even raise the ductwork upon slats at no charge to me.

Opinions greatly appreciated.

Thank you,

Ivan Vegvary

One thing to think about...
I learned by accident that insulation is HEAVY.
IN particular, cellulose insulation looks cost effective, but
is heavier than
fiberglass, BUT as it ages, it absorbs moisture and becomes
MUCH heavier. *Depending on the construction of your ceiling
and how well it's attached, this may become an issue.
I was planning a DIY cellulose installation. * Glad I didn't.

I'd at least ask the question of your contractor.

Good point! As it happens, this is an old house with weird
construction. All of the ceilings have 1/2" plywood on the bottom
covered with 3/8" drywall. Structurally very sturdy. While I
certainly try to stand on joists only, I am able to stand on the
ceiling and not break through, even at 230 lbs.

As one who just stepped though his own ceiling, for the first time in
27 years and more than 100 trips to the attic, I'm jealous.

Thanks, Ivan Vegvary