insulatng return duct in attic

Posted by on October 7, 2006, 5:12 am

I have a centrl air unit installed in the attic; I was recently going
duct by duct to make sure all connections were tight and insulated -
during this process: I noted that the return duct which draws air from
inside the house was insulated for the first few feet but then ran
across the attic uninsulated until it went back into the unit. Am I
mistaken or should the return that passes through the super heated air
of the attic also be insulated? I spoke to a contractor friend of mine
and he said it is common not to insulate the return - but it just seems
wrong to me...

Posted by daytona on October 7, 2006, 6:13 am

does not have to be....it's choice.

>I have a centrl air unit installed in the attic; I was recently going
> duct by duct to make sure all connections were tight and insulated -
> during this process: I noted that the return duct which draws air from
> inside the house was insulated for the first few feet but then ran
> across the attic uninsulated until it went back into the unit. Am I
> mistaken or should the return that passes through the super heated air
> of the attic also be insulated? I spoke to a contractor friend of mine
> and he said it is common not to insulate the return - but it just seems
> wrong to me...
>

Posted by Steve Scott on October 7, 2006, 8:18 am

Is there any heat gained or lost through the uninsulated duct? IOW,
is the temp of the air in the duct higher or lower than the
environment it's in? Almost certainly the answer is yes. So, yes,
the duct should be insulated and sealed. If the exposed portion isn't
sealed I'd strip the insulation off the rest of it and seal and
insulate the whole thing.

It may be common to not insulate it, but that doesn't make it right.
The return air is maybe 80 degrees and the attic 120 or higher.

On 7 Oct 2006 02:12:17 -0700, jbgalligan@gmail.com wrote:

>I have a centrl air unit installed in the attic; I was recently going
>duct by duct to make sure all connections were tight and insulated -
>during this process: I noted that the return duct which draws air from
>inside the house was insulated for the first few feet but then ran
>across the attic uninsulated until it went back into the unit. Am I
>mistaken or should the return that passes through the super heated air
>of the attic also be insulated? I spoke to a contractor friend of mine
>and he said it is common not to insulate the return - but it just seems
>wrong to me...

--
We have met the enemy and they are us
and you are me and we are all together
--Walt Kelly and the Beatles

Posted by udarrell on October 7, 2006, 10:58 am

Steve Scott wrote:

> <>Is there any heat gained or lost through the uninsulated duct? IOW,
> is the temp of the air in the duct higher or lower than the
> environment it's in? Almost certainly the answer is yes. So, yes,
> the duct should be insulated and sealed. If the exposed portion isn't
> sealed I'd strip the insulation off the rest of it and seal and
> insulate the whole thing.
> It may be common to not insulate it, but that doesn't make it right.
> The return air is maybe 80 degrees and the attic 120 or higher.

Right-on Steve, - the temp split could be even more, like 130 or 140-F
to 72-F.
The larger the temp differential the more heat transferred.
In the winter the opposite situation also needs the insulation.

Also, on the off cycle the air in the duct could be a heat-overload on
the A/C system.

- udarrell

--
Air Conditioning's Affordable Path to the "Human Comfort Zone Goal"
http://www.udarrell.com/airconditioning_eer_ratings_over_seer_ratings_central_systems.html
(Solving ESP)
http://www.udarrell.com/udarrell-air-conditioning.html

Posted by Bubba on October 7, 2006, 10:36 am

On 7 Oct 2006 02:12:17 -0700, jbgalligan@gmail.com wrote:

>I have a centrl air unit installed in the attic; I was recently going
>duct by duct to make sure all connections were tight and insulated -
>during this process: I noted that the return duct which draws air from
>inside the house was insulated for the first few feet but then ran
>across the attic uninsulated until it went back into the unit. Am I
>mistaken or should the return that passes through the super heated air
>of the attic also be insulated? I spoke to a contractor friend of mine
>and he said it is common not to insulate the return - but it just seems
>wrong to me...

As long as your unit is big enough and you have plenty of cash for
your utility bills, then everything is right with the world.
Make sure your uninsulated return isnt insulated from the inside and
you just dont see it.
Bubba

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