Flex AC/Heating Duct repair?

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May 22, 2013
Hello All,

I am wanting to get prepped for winter this year, last year my bills were outrageous. My flex duct-work is an overall mess. Too many bends and folds, a lot of ups and downs(not enough hanging points).

MY duct work runs under my house.. in a crawl space.. the first year I lived in the house I had a mouse invader who chewed at least one hole in the duct work(fixed kinda with duct tape).

I plan to find more holes, what is the proper way to seal the holes in the duct work, if any? I imagine I want to re-insulate it some how.. and re-seal the duct.

You can try to get some spray glue foil tape and mastic (duct sealant, it's like cast), if they are not too badly damaged. If they tears are too big the only way to fix them is to replace them. Make sure they use mobile home style flex ( black flex, not silver ), it's a lot more durable.
If it's that bad, you might want to consider replacing it & going to a higher R-value.

To minimize restrictions, it must be pulled taunt and sufficiently supported. Otherwise, the air will actually 'swirl' through it, causing turbulence. Think of it as "UUUUUUUUU" with peaks and dips as opposed to "_________" (straight & flat).

Any tape you use should be rated UL-181. I'd recommend the metal tape. The duct surface must be free of dust/dirt.
Tear it all out and run hard pipe. Flex duct was not designed to be used for full duct runs, only a couple of feet before the registers for noise control.
Regardless of what its original intended use was it is used for the entirety of ductwork in houses around here and has been for at least thirty years.

It does not last forever. At some point it does have to be replaced.

There is nothing wrong with it. If you want to replace your flex with rigid duct you are in for quite a job and no insignificant expense. I buy a lot of R-8 flex duct which has been put into building codes in a lot of areas in the South. In Ohio R-6 is still OK and, in some cases, they still use R-4.
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