Flex duct R value, Does it really matter in my application?

[Unregistered-ama1az]

I am getting ready to replace the flex duct in our attic. There are numerous places were the plastic outer layer has torn and insulation is falling off the duct.
Since this will be the second time in 3 years part of the duct work requires replacement, I intend to replace all the plastic covered duct with foil covered duct.

It seems I have two choices readily available to me after checking the local home improvement stores and an a/c supplier.
It is either R4.2 or R6.0. I understand that the higher R6.0 value equates to better insulation. But, it will also cost $200+ more than the R4.2 to redo everything.

My home is located in Phoenix, AZ. All the ductwork is located in an unconditioned attic. The attic is vented by gables and whirllys. The duct is entirely suspended from the trusses because of the high roof pitch and vaulted cielings. There is no additional insulation touching the duct. The longest run of duct will be no more than 35ft.

Basically, will I see a noticeable difference between the R4.2 and R6.0 duct to justify the extra money?
If not, I just assume spend the money my next project…re-insulating the attic. The money will go a long way there.
Thanks,
Alan

[doug seibert]

How’s the cooling in those far rooms…..Flexible ductwork slows the A/C……long runs should be avoided especially long drooping suspended runs………

And what’s the cause for the repeated damage to the existing flex ductwork…..maybe you need something tougher…….?

Do you have access to replace with insulated rigid pipe or ductboard ?

[Unregistered-HKestenholz]

If this damage is repeated; get larger sheetmetal ductwork and pull the flex duct through it inside. Just some pieces would need replacement, cutting cost. Mastic sealer and tape outside would prevent moisture from getting to the inner layer. The flex duct would be better-supported.

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