IFGC 503.10.1 General. A vent connector shall be made of noncombustible corrosion resistant material capable of withstanding the vent gas temperature produced by the equipment and of sufficient thickness to withstand physical damage.

NFPA 211 dittoes this but adds if corrugated, must be listed. This is due to decreased flow capacity by corrugated ducts.

I recently ran to a hardware store to get some vent connector and all they had was cheap aluminum flex, like you see with dryer vent kits. Its tag stated it was rated to 480F. I told the homeowner it was suitable for an overnight repair but that was it. This duct does Not meet the requirements for physical damage. Moreover, it comes apart really easily. It is so sloppy, it cannot hold its shape and needs much more support than rigid pipe. You need slings. If you try to screw through a "drive' into it, the flex just crushes and comes apart. Real junk. All it's good for is making robot arms for the kid's school play...

Make sure it is not a listed aluminum flex connector, which has listing stickers on it and is much more rigid and substantial than dryer vent flex.

HTH

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