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Old 03-02-2010, 11:48 AM   #1
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Air flow and displacement


In a home of approximately 3000 sq. ft. with a 5 ton HVAC there're 8 output flex duct too various parts of a C shaped home. My question is concerning the design of the plenum box that has a 10" flex input from the main it feeds three outputs a 9" and two sixes (6"). Note: the box is presently 23"x23"x14". Because the design of the system appparently donot allow for maxium output to the bathroom which uses one of the 6" out Flexes, I wish to redirect flow and increase it. Note: All Flexes is R8.

I want to decrease the box fed by a 10" duct from the main plemun which has 8 outputs 4 on top and 4 on the side. From 23x23x14 to 16x16x18 which is 61% of the original. Note I was told this would increase the flow. Then I want to change the two 6" ducts to one 7" and 5" ducts which feeds the bathroom (7") and the office (5"). The bathroom has two skylights which are 20"x20" appiece.

What would be the affect of the volume of air provide to the bath when compared to 7" to the 6".


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Old 03-02-2010, 06:22 PM   #2
An old Tradesmen
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Air flow and displacement

Decreasing the size of that box, will decrease air flow.

The 10" that feed the 9" and 2-6" is too small. Increase it to a 12" at least, and you will get better air flow.

Your probably also short on return. Increasing return air will give you more air to all supplies.

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hck2010yah (03-04-2010)
Old 03-04-2010, 06:02 PM   #3
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Air flow and displacement

Advice well taken!
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