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Duct trunk sizing

Posted by Jackfrost069 (My Page) on
Thu, Feb 28, 13 at 15:41

I have two heat heat pumps in my house, one upstairs and one downstairs. Both are two ton units.. Upstairs is 995 sq. ft. And downstairs is 880. I am going to replace the ductboard with metal trunk. The duct calculator slide rule calls for an 8x18 trunk downstairs, and an 8x20 upstairs. Does this sound right? There are 11 takeoffs downstairs and 12 upstairs.


Follow-Up Postings:

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RE: Duct trunk sizing

That looks close, for ductboard, might be a little noisy for metal. I hope the entire run of trunk isn't going to be all one size?


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RE: Duct trunk sizing

Not really sure. I don't have a duct sizing program in order to determine the step down size. There is a ten foot run on one side of the plenum, and a 15 foot run on the other, as it is right now. The ductboard is 10x12, I think. It seems ok downstairs, upstairs doesn't seem to be putting out adequate airflow.

This post was edited by Jackfrost069 on Thu, Feb 28, 13 at 17:58


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RE: Duct trunk sizing

lot of work for a not really sure install.

"I hope the entire run of trunk isn't going to be all one size?"

I wondered about that myself.

why not get advice from a pro in your area who
can visually acess what you have??

what is the reason for removing old trunk line?
is poor air flow upstairs something new?

best of luck.


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RE: Duct trunk sizing

Thanks for the follow up, guys! No, the airflow problem upstairs has always been a problem. I'm not really comfortable with ductboard, I've heard it can release fiberglass fibers into the air. I'm thinking of having someone come out and take a look at it for me.


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RE: Duct trunk sizing

when you work with ductboard, cutting into
it, it releases fg particles. once installed
this doesn't happen..unless duct board
is cut into.
if it has been there for a while, is in good
shape, and performs well...why change it??

ductboard plenums have been around
a long time, and are still made on site
in new installs.
it is a good product.

Instead, invest that $$ into solving air flow issues.
sealing ductwork has immediate effect & pays
for itself quickly.

best of luck.


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RE: Duct trunk sizing

Hey, thanks a bunch for the help! Greatly appreciated!


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