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Old 01-12-2013, 03:32 PM   #31
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Ok so I don't have to build a box out of the duct board for these plenums. Just the flat piece for the bottom of the plenum correct?

Would mastic be the way to go to seal it to the wood? I have a roll of aluminum faced 181-A tape as well.

I'd prefer to have a little up in the ceiling joist because I'm installing furring channels to the bottoms of the ceiling joists.

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Old 01-12-2013, 03:37 PM   #32
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The duct board has to have some of the board trimmed from the edges(1-1/2") so that it fits into the joist space, and those edges then stapled to the joist. Then you can mastic it. Let the furring help support the duct board.
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Old 01-12-2013, 03:49 PM   #33
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Oh ok gotcha. So you're saying trim it then staple it to the bottom of the joist? Or can i get it properly sealed up in the joist cavity about say an inch?
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Old 01-12-2013, 04:11 PM   #34
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Oh ok gotcha. So you're saying trim it then staple it to the bottom of the joist? Or can i get it properly sealed up in the joist cavity about say an inch?
If you stick it into the cavity an inch, you are greatly educing your return air flow more then it already will be by the 1" thickness of the duct board. And have to add more return elsewhere. So no, don't stick it up in the cavity by another inch.
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Old 01-12-2013, 04:14 PM   #35
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Ok no problem. Is the duct board pretty plush or is it more stiff?
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Old 01-12-2013, 04:16 PM   #36
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Fairly pliable.
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Old 01-12-2013, 04:26 PM   #37
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Alrighty I found a place here in my home town that sells it, so will be picking it up Monday. Is there a certain brand of mastic you'd recommend?
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Old 01-12-2013, 04:50 PM   #38
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No, its all about the same.
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Old 01-12-2013, 04:53 PM   #39
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Gosh man I thank you so much for being patient with me and helping me through this.
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Old 01-12-2013, 06:29 PM   #40
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Your welcome.
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Old 01-13-2013, 11:18 PM   #41
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So Aluminum faced tape is not needed to seal the duct board pieces together just the mastic?

Will UL 181B-FX tape work if it is needed?
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Old 01-14-2013, 09:37 AM   #42
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Been There, How does a circle move more air that an oval? Less Turbulence?

And what is the loss due to shape? It seems like square, and right angles

would be the worst to me because of the 90 degree corners, no?

Just wondered.
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Old 01-14-2013, 02:57 PM   #43
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So Aluminum faced tape is not needed to seal the duct board pieces together just the mastic?

Will UL 181B-FX tape work if it is needed?
Mastic and tape.
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Old 01-14-2013, 03:01 PM   #44
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Been There, How does a circle move more air that an oval? Less Turbulence?

And what is the loss due to shape? It seems like square, and right angles

would be the worst to me because of the 90 degree corners, no?

Just wondered.
Air tends to move in a circular motion. An oval is not round, so the circular motion is done in a smaller area.

A 6" oval is equivalent to a 5" round pipe.

A 6"X6" duct has more free area then a 6" oval or circle does.

A 6" circle is 28 sq inches. A 6"X6" duct is 36 sq inches.
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Old 01-14-2013, 04:53 PM   #45
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One end of the board will be female the other male. Run a bead of caulk in the female, then when you insert the male it will seal. I use a duct staple to staple the male's flap to the female and then mastic it.

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