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Adding duct for addition and can’t follow the 2 foot rule Advice

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DavidWA

Mechanical
Aug 28, 2022
1
Hi, if I’m adding duct 10” to run to the attic
in 3 ton down flow furnace when all ducts are in the crawl space
that the opening will be exactly under the coil but very close to it at the base can ( I cannot / have no space to have 24” inch run/space and than to cut the opening) so the opening again will be very close
1) how much cfm will be in that 10” duct metal round
will it be around 300 cfm
2) also do I need to insert like 45 elbow inside the can base to direct the flow to that duct
or just open that base can and 90 elbow from the base can will be enough
 
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Can you please sketch it up?

Your description is a little confusing.
 
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