Original message
| beatle
|  "return duct sizing"
, posted Tue 13 Jul 21:31  
I recently ran into a deal where I work where I have to penetrate a firewall to put in some return ducting to an air handler. Problem is I don't know the formula for the hole size. I do know the cfm for the three rooms. this building has a ceiling return,but the original contractor put up a firewall instead of a penetration. THis seems to be a typical problem with low bid contractors in the n.c. area as far as schools go.
BEATLE
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Replies:
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| bwildrick
| "Re(1):return duct sizing" , posted Mon 11 Jul 10:41
If in fact that is a fire wall (defined as a 2 hour rated separation by New York Mechanical code) there has to be a fire damper in it. There also needs to be a fire damper in the opening of a 1 hour rated partition if there is no duct attached to both sides. mcquay.com has a duct sizer that you can download or use your hand held ductulator. The computerized one is nice for those in between or borderline sizing issues.
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| Hal_C
| "Re(1):return duct sizing" , posted Thu 15 Jul 16:36
Don't you have to install fire dampers in the the duct where you penetrate a fire wall.
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| Xenos
Webmaster 
| "Re(1):return duct sizing" , posted Tue 13 Jul 21:41
I don’t know the formula, I cheat and use a ductulator.
Xenos.
The best way to escape a problem is to solve it.
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