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  #1  
Old 02-05-2007, 08:11 PM
big_willie big_willie is offline
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Howdy All

I am new to the trade (about a 14 mo.) and a few weeks ago I started taking plans and specs home to study. I found a situation were the engineer did not size the duct work but provided a note to size duct to 11.5 S.F. coordinate with ceiling height. I asked my foreman what this was and oddly he did not know. He said the shop people would figure this out and not worry about it. He is a bit of a hillbilly (don’t get me wrong he is very good at installing duct however; I just have this need to know how things work).

BTW this is a R/A transfer. Can someone here please, school me as to what he is looking for? I get the coordination part; we have 16’’ from structure to ceiling.


Kind Regards,

Bill
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Old 02-06-2007, 05:59 AM
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I'm thinking he wasn't sure on the area above the ceiling and therefor letting you make the decision on the l x W of the duct to accomadate the plenum area above the ceiling.

Just my thought?
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Old 02-06-2007, 06:00 AM
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Quote:
Originally Posted by Bud
I'm thinking he wasn't sure on the area above the ceiling and therefor letting you make the decision on the l x W = 11.5 SF of the duct to accomadate the plenum area above the ceiling.

Just my thought?
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Old 02-06-2007, 06:32 AM
tnbndr tnbndr is offline
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big_willie:
I have learned the hard way to never guess what someone's intentions are. The best bet is to call the engineer and explain that you want to do things correctly and don't quite understand what he is asking for. I have found most to be quite understanding.
Most engineers give a velocity or pressure drop to size the ductwork to if it needs to be changed in size or if the size has been omitted.
As Bud says it appears that he is giving you the square footage of duct for you to size to fit in the space allowed. If you only have 16" you would have to size the duct 12" deep if there are no lights. (?"x 12")/144 = 11.5 would end up being a 138" x 12" duct = BAD aspect ratio. You would need to know the amount of CFM you are trying to return or transfer. If it is indeed a transfer the normal velocity for sizing is around 300 fpm. A ducted return from an air handler is usually sized at 2000 fpm or 0.15 pressure drop/100' of duct.

Make the phone call.
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