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Old 07-02-2014, 01:59 PM   #1
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flex duct recommendations


I am going to replace a 25' run of flex duct that is in poor condition and was wondering if there are certain features or options to be aware of. I noticed that 25' is about 30 dollars for R6 insulation from the big hardware giants and then I saw the following on Amazon;

[ame="http://www.amazon.com/Dundas-Jafine-BPC625R6-Insulated-Flexible/dp/B0049H997K/ref=sr_1_1?ie=UTF8&qid=1404322637&sr=8-1&keywords=flex+duct"]http://www.amazon.com/Dundas-Jafine-BPC625R6-Insulated-Flexible/dp/B0049H997K/ref=sr_1_1?ie=UTF8&qid=1404322637&sr=8-1&keywords=flex+duct[/ame]

The above is R6 as well, so I am not sure why it is almost double the price. This specific duct run exits plenum and shoots up and over an arch in the attic. Nothing is supporting the duct, it appears to be just flung over, so I am suspecting this is impacting air-flow. It is difficult to gain access to the other side that the current flex duct shoots down, so I am not aware of how bad the other side is yet. Are straps the best choice for supporting such runs that traverse over and then drop down?

Any recommendations or things to watch out concerning flex duct would be appreciated.

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Old 07-02-2014, 02:32 PM   #2
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flex duct recommendations


Yes, they make hangers for flex. Use as many as you can to keep the flex straight. Oh one more thing be sure to wear gloves and a mask. That fiberglass is nasty.

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Old 07-02-2014, 02:42 PM   #3
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flex duct recommendations


Make it only as long as needed and cut off excess. If you have had airflow problems in that area, this would be a good time to increase the size.
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Old 07-02-2014, 02:56 PM   #4
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flex duct recommendations


Quote:
Originally Posted by McGee View Post
Make it only as long as needed and cut off excess. If you have had airflow problems in that area, this would be a good time to increase the size.
A big 10-4 on the air flow problems through this duct. There are a lot of variables that I am addressing:

- bad damper motor for zone control system on this duct
- kinked at top of arch with no hanger straps being used
- several patches/holes in existing flex duct.

I have not measured the existing duct size, but I would guess it is 6 or 8 inches. Is there a way to determine the size of the duct w/out cutting open to remove insulation around duct? Hypothetically speaking, if the current duct work is 6", I am guessing you might recommend 8 inches?

My concern is the connection to the plenum - how do you go from 6" to 8", while still having to fit the same connection to the plenum?
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Old 07-02-2014, 03:36 PM   #5
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flex duct recommendations


You can measure it at the register. Just take the grill off. It is not hard to increase the plenum opening. Tin snips will work if it is metal, then install the proper collar. You can buy reducers, but if you use it at the beginning of the run you will lose a lot of your gained air flow. Using a reducer should be avoided but it isn't as critical at the end of the run. If you have 6", I would go 8" if your lacking flow. 2" makes a lot of difference.
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