Combining two 8" ducts

tynman11November 14, 2012

Hello, if combining two 8" ducts should I use a 8x8x10 wye or a 8x8x12 wye? Thinking the 10" wye even though it'll be slight less cfm than the combined cfm of two 8s

I'm upgrading ducting and looking to combining two supplies that are in one room.

Also two returns, and 8" in one bedroom and another 8" in a bedroom, across the hall.


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I am assuming you talking round duct. Try 14" dia. to the first drop and 8" to the other.I would not undersize it.

    Bookmark   November 14, 2012 at 6:14PM
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Flex duct. I'm confused, 14" is about 750cfm and 8" is about 160cfm. I adding to 8" returns so that's 320cfm, but a 14" and and 8" is 910cfm.

Would it make more sense to use a 12" wye? That would be 320cfm (2 8") connect to about 510 cfm (1 12"). I'm not sure if that extra 190cfm will be an issue or not though.

    Bookmark   November 14, 2012 at 6:25PM
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