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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. enter image description hereenter image description here

  • Regardless of industry recommendations or others' advice, always obey "MOM" (manufacturer's operating manual). – Jimmy Fix-it Mar 31 '18 at 14:43
  • Let's be sure to distinguish between metal flex duct (as in the aluminum semi-rigid in the first photo) and Mylar foil hose (as in the second photo). These are not both "metal" ducts. – isherwood Sep 11 '20 at 12:47
  • Your head is in the right place if you are keeping an eye on the UL certification of these ducts. It's really unfortunate that big box stores will stock non-certified fire hazard ducts right next to the certified ones. Semi-rigid 4" ducts are OK if UL certified. The absolute best option though is to use rigid metal duct for the entire line. No matter what though, UL-2158A... – Z4-tier Oct 12 '20 at 2:30
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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.

  • That’s a good point about gases. What about the semi-rigid, and how it gets all bent, and with apparent breaks at corners? I was worried since this is a tight space, it keeps getting compressed, and further bent and contorted – Michael Mar 31 '18 at 23:12
  • That is what I was referring to as aluminum flex. All those ridges reduce air flow and it is easy to smash. That being said it is the most popular for ease of use and at least in my area is code compliant. I still prefer hard metal pipe when at all possible. Making the final connection is often challenging but worth it in my opinion. Improperly ducted dryer vents are probably why your association requires cleaning every 2 years. I just looked at mine which is 100% galvanized iron pipe with no screw penetrations and it is perfectly clean after 15 years. It keeps the velocity up, removing lint – user76730 Apr 1 '18 at 0:44
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    I believe dryer manufacturers don’t like the foil ducts because they can’t contain a fire. I recommend looking into a Dryerbox (google it, available on Amazon and big box stores). It helps prevent the hose from kinking and makes a cleaner vent area. – KVL May 14 '20 at 16:14
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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:

https://www.lowes.com/pd/Lambro-24-in-to-41-in-Adjustable-Periscope-Dryer-Vent/4566306

https://www.homedepot.com/p/Everbilt-28-in-to-45-in-Adjustable-Space-Saver-Aluminum-Dryer-Vent-Duct-UD48HD/203632347

  • The product from Lowes is not UL certified, and while I couldn't find anything about certification on the HD product, I'd be willing to be it is not UL certified either. Also, and I might be misinformed here, my understanding is that dryer vents are supposed to be exactly 4" for the entire length of the run; any bigger reduces velocity and leads to lint buildup, while any small is bad for obvious reasons. – Z4-tier Oct 12 '20 at 2:38

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