Can some one tell me the effects that occur when the plastic sheathing on flex ducting disintegrates. Leaving just the insulation covering the duct. I would really appreciate any help.
Further deterioration at an accelerated pace.
Hi all,
the big problem here is that when the outer jacket is missing or damaged moisture will start to condense against the insullation turning into one big sponge trapping water, when this reaches its maximum capacity it will start to drip ruining ceilings etc.
Regards
Gerry
Thanks for the help gentlemen. I appreciate it. Why do the flex ducts have to be suspended from the rafters? As opposed to laying on the floor of the attic.
I had a home owner ask me. The reason I came up with was…
The insulation will not provide full coverage.
Also, the ducting may not get full airflow through it.
Are there any other reasons I should know about?:neutral:
I didn’t know they did. Now I’ll have to go back and correct thousands of inspections or hope that I don’t get sued. 
I think you’re confusing ducts in the crawl space with ducts in the attic. Ducts in the crawl space should be suspended instead of laying on the ground. Ducts in the attic can lay on the attic floor, crawl up the walls, hand from the roof, whatever.
I believe SMACNA, ASHRAE and the duct manufacturers have specific guidelines regarding duct supports to prevent kinking and I also believe many HI’s don’t know what to look for. I know I don’t, other than supports needed every 5’ and I do find kinked and obstructed flex duct occasionally. I think I’ll try to find a good CE course on HVAC including ductwork.
Here is the “Air Diffusion Council” installation instructions for flex duct. It appears to be the same instructions that ATCO, the largest mfg of flex duct, includes with their ducts. See figures 10 & 14:
http://www.flexibleduct.org/download/ADC~Inst.pdf