I pulled my dryer, and am reinstalling it. It had a semi-rigid metal transition duct, which was all bent out of shape, and looked like it had some holes forming (see pic). I did homework, and read a site talking about how the aluminum foil transition ducts are the only ones UL listed, and at least at Home Depot that was true, the semi-rigid were not UL listed (except for the expensive GE dryerflex one). So I installed the foil duct, and after taping the ends and getting everything set, I turn around and see a warning sign on my Kenmore dryer saying don’t use Metal Foil ducts to vent. Does this include the transition vent? If not, why couldn’t I use the foil vent? Is it something specific about this dryer? In general, the info out there on transition vents are all over the place in terms of rules and suggestions, looking for some concrete expertise. I probably wouldn’t thought much of it, but a neighbor just recently had a dryer fire in their home, so it’s on my mind, and I want to get this right. In our condo association, we are required every 2 years to have a professional dryer vent cleaning.
Gas driers must use metal vent. I prefer actual metal pipe. Aluminum flex reduces air flow significantly and even if not dangerous will lengthen the time it takes for cloths to dry. Gas driers have carbon monoxide flowing through the vent. Would you want your water heater or furnace vent using foil venting material? Granted a clothes drier vent doesn’t get as hot but if it rips that would not be good.
If a tight installation is part of the problem - There is another style of transition connection called a "periscope vent" which is all metal and cannot be easily punctured or collapsed. They come in sizes, and with snips and foil tape can be customized if need be.
Here are some examples: