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Reuben Saltzman

Dryer Transition Ducts: Is Foil Better Than Semi-Rigid Aluminum?

I’ve always told my clients that the best type of dryer duct material is a completely rigid metal duct, with as short of a run as possible.  I’ve recommended using semi-rigid metal when necessary, as a way of transitioning from the dryer to the duct.  Semi-rigid aluminum is all that anyone recommends!

  • There was an article published in the ASHI Reporter in April 2005 saying that semi-rigid metal was the only good substitute for smooth metal (click here to see it).
  • If you search online for the best type of dryer duct, the only advice you’ll get is to use semi-rigid aluminum as a transition.  This information is repeated on every web site or blog dealing with dryer duct safety.

After doing some research on the semi-rigid transition ducts, I’ve learned that they might not be allowed in Minnesota.

To understand why, you need to know the difference between a clothes dryer duct and a transition duct. They’re not the same thing, and they’re not interchangeable.  According to the Minnesota Mechanical Code, a dryer duct is required to be constructed of metal, and can only have a smooth interior finish (section 504.6).   This means that flexible materials are not allowed for dryer ducts; not foil, not semi-rigid aluminum.

transition duct is flexible, which allows the dryer to be connected to the duct, then pushed back up against a wall so it’s not sitting in the middle of the room.  A transition duct is allowed by the Minnesota Mechanical Code to connect the dryer to the dryer duct… but that’s all.  These transition ducts are limited to single lengths of eight feet or less, and must be listed and labeled for the application.

Keyword: Listed

I went shopping at a few retailers for dryer transition ducts, and I was quite surprised to learn that the semi-rigid material I’ve always recommended is not a UL listed product!  If there are any manufacturers that do make a UL listed semi-rigid duct, they’ve done a good job of hiding their products – even online.

Semi-Rigid Metal Duct
Semi-rigid aluminum duct

Home Depot sells ‘dryer stuff’ from Deflect-o, while Menards and Lowes sells ‘dryer stuff’ from Dundas-Jafine.  After browsing through Deflect-o’s web site and Dundas-Jafine’s web site, I learned that the only UL listed dryer transition ducts are the ones that look like they’re made from foil, pictured below.  These transition ducts are actually made from aluminum.

UL Listed Dryer Transition Duct
UL Listed Dryer Transition Duct (foil)

Interesting.   I won’t be reporting the semi-rigid stuff as unsafe – I have it in my own house, and I feel like it’s perfectly safe… but if it’s not listed, it’s a code violation and I won’t recommend it any more.

I wonder why the semi-rigid material isn’t listed?

Reuben Saltzman, Structure Tech Home Inspections – Email – Minnesota Home Inspections

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No responses to “Dryer Transition Ducts: Is Foil Better Than Semi-Rigid Aluminum?”

  1. David Framowitz
    June 18, 2010, 3:58 am

    I red your comments about clothes dryer transition ducts and flexible corrugated aluminum ducts and your question as to why aren’t the flexible aluminum ducts UL listed.

    The answer is simple – the flexible corrugated aluminum ducts do not meet the requirements of UL2158A and therefore can not be listed as a dryer duct.

    You see, in order to be listed as a UL listed dryer duct, the ducts have to pass all of the required tests of UL2158A, including the crush and puncture test. These flexible corrugated aluminum ducts which are sold by all of the major retailers, including those manufactured and sold by Whirlpool, easily crush and puncture. Not only that, they actually unravel at the edges which can be a danger to those handling these ducts.

    Once these flexible corrugated ducts are crushed, or punctured or have unraveled edges they are a danger to the household (lint build-up which can cause overheating of the clothes dryer and subsequent dryer fires) and therefore should not be permitted or used.

    That’s why the 2009 ICC Mechanical Code only permits the usage and installation of UL 2158A Listed Clothes Dryer Transition Ducts.

    Best regards,

    David Framowitz
    GLV International Ltd.
    Ein Vered, Israel

  2. Reuben Saltzman
    June 18, 2010, 4:07 am

    Thank you for the great information, David. Very helpful.

  3. david fass
    February 9, 2012, 8:49 am

    That does not explain why the foil ducts are UL-listed. Are the spring-reinforced foil ducts somehow more robust than the semi-rigid ducts? I really don’t think so. I wonder if the foil ducts have somehow slipped through a loophole in the standard.

  4. Reuben Saltzman
    February 10, 2012, 5:00 am

    I’d love to know the answer, David. Clothes dryer manufacturers only allow the flexible metal, non-UL listed transition ducts… so what is a homeowner supposed to use?

    February 29, 2012, 6:49 pm

    i am trying to figure out on the vent hose itself
    if we have one that is ul2158 rated–it is a pro flex
    aluminum foil duct by dundas and jafone–is this
    approaite to use w/ all our dryers we sell– do we
    need to cut the length down from 5 ft or 8ft for saftey

  6. Reuben Saltzman
    February 29, 2012, 8:14 pm

    Hi Cindy,

    Hi Cindy,

    Yes, the Pro-Flex aluminum foil duct by Dundas Jafine is UL Listed, however, many dryer manufacturers prohibit the use of foil ducts, even when they’re UL Listed.

    I recently sent an email to several dryer manufacturers asking them about this, and the only one that responded was someone from Whirlpool by the name of Lee Herendeen; he was very helpful.

    He sent me a link to this product – . This is the first semi-rigid, UL Listed dryer transition duct that I’ve seen.

  7. MaryAnne
    June 28, 2012, 5:53 am

    Okay. I’m still confused. I need to replace the duct from my dryer to the outside vent. It is approximately 20′-25′ long, and goes up from the dryer (about 8′) into the attic and runs along the attic to the vent located on the side of the house. I have found a 20′ and 25′ flexible duct online, however, after reading this post I am under the impression that these are not safe even if they are UL listed?? Can you please tell me the best, safest way to replace this duct, as well as where I can purchase the materials I need? I truly appreciate your help and expertise.

  8. Reuben Saltzman
    June 29, 2012, 3:59 am

    MaryAnne – you say you found a 20′ and 25′ flexible UL Listed dryer transition duct online… would you mind sharing the link with me? I was sure that there was no such thing. The longest flexible section of UL Listed dryer transition duct that I’ve ever found was 8′ long.

    At any rate, the only thing you should be using in your attic is rigid metal duct material. You can purchase this material at any home improvement store.

  9. Gil Searcy
    September 13, 2012, 9:16 pm

    Reuben -I happened upon your blog and thought I’d share some facts regarding UL Transition Duct. I work for the leader of the dryer venting industry, Builder’s Best, Inc., and can clear up some of the concerns in the blog.

    “Dryer Duct” is ductwork from the wall and ending at termination.
    “Dryer Transition Duct” is ductwork from the dryer to the wall.
    So, when determining types of material acceptable by building codes and dryer
    manufacturers, this terminology is important to understand.

    Oddly enough, foil duct passes a UL Transition Duct standard only because the test was designed for it to do so. UL doesn’t even approve it for dryer venting, they only approve to pass the tests under UL2158A. They basically took the UL181 (HVAC) testing procedure and added an impact and a flame test.The impact test is the most ridiculous one. Drop a 15lb sand bag on the duct, remove it, then determine if the cross section of the duct has experienced cross-sectional area reduction in excess of 25%. Somehow this doesn’t seem realistic since a 150lb dryer doesn’t bounce back after you crush the foil duct against the wall.

    There is a semi-rigid UL Transition Duct Kit available by GE at Home Depot in the appliance department. It is manufactured by Builder’s Best, Inc. Builder’s Best is by far the leader in dryer venting products and have been selling this UL product to professional installation groups as needed for 10 years. It’s not that prominent at retail due to the cost, but is gaining more acceptance in the market.. Below is a link to the UL dryer duct on Builder’s Best website:

    We have components like the patented Close Elbow and Soft Cuff (slit) duct ends to
    make it easier to work with semi-rigid duct.

    Gil Searcy
    Builder’s Best, Inc.

  10. Reuben Saltzman
    September 14, 2012, 3:45 am

    Hi Gil,

    Thanks for sharing the impact testing requirements of UL2158A. What are the flame spread requirements?

    I don’t recall finding any UL Listed semi-rigid dryer transition ducts at any of the Home Depots in Minnesota, and trust me, I’ve looked. They seem to use different vendors, depending on what part of the country you’re shopping in.

    Do you have a link for people to purchase this product? I’d be happy to add a link to your product on this blog post – .


  11. Reuben Saltzman
    September 14, 2012, 3:51 am

    Funny, I just searched at with the term “2158A” and found a UL Listed semi-rigid transition duct.

    Why couldn’t I find it before? Because the description doesn’t have the word “dryer” or “clothes” in it. .

  12. chris cooper
    March 19, 2013, 8:59 am

    I deal with a lot of moisture issues resulting from deficient dryer ducts built of all sorts of dubious materials. Usually the biggest problem is that the duct is too darn long, and it runs though cold attic space to it’s terminus. During cold months the condensation build up is UN-believable. and it creates a nasty cascade with the lint collection.
    (think 4″ diameter ice & lint popsicles )

    All the products marketed for dryers cater to the ideal scenario where your dryer is 8′ or less from the terminus (although it IS possible to purchase 25′ length of De-flecto transition flex.)

    I’ve replaced a some ducts with rigid galvanized, foil taped joints and insulated them with Reflectix.
    There is still a problem at the wall jack. As far as I know there are no wall jacks designed to cope with the condensation that results from such long runs, and the situation fosters rot in the plywood sheathing.

    I’m beginning to think part of the answer lies with semi-rigid flue liner, but a bull dozer sounds more attractive

  13. chris cooper
    March 19, 2013, 5:06 pm

    What do you suppose is better? 25 foot run of 3″ smooth pipe or 25′ of 4″semi rigid flue liner?

    this is a vertical with 2 90’s at the transition zone.

  14. Reuben Saltzman
    March 20, 2013, 3:38 am

    Chris – if I had my choice, I would probably opt for 25′ of 3″ smooth. I think this would have less of a potential for getting clogged.

  15. Bruce Egilson
    April 19, 2013, 1:00 am

    I have found that the semi-ridged ducting is not flexible enough as a transition duct. My attempt to use it resulted in it bursting apart when pushing the dryer into place because it was required to to do a full u-turn.

  16. Bobby
    April 26, 2013, 11:33 am

    Be ready to be amazed! Did you ever hear of DRYER FLEX?! It has the benefits of workability like the slinky foil, but also the fire resistence (Class 0 listed) and air flow efficiency of the semi-rigid. If you are a non believer, then go to and watch the video. For more info, send me a email at

  17. Reuben Saltzman
    April 26, 2013, 11:44 am

    Hi Bobby, I tried that stuff out almost a year ago. You’re right, I was amazed. You can see what I wrote about it here:

  18. Bill White
    July 14, 2013, 12:47 pm

    Hi Reuben, my dryer vents directly out the back and into the wall, a distance of about 6 inches. It was installed with flex semi rigid duct. I want to replace it with Dryerflex. I have not seen any comments about cutting this material. If I buy the 36 inch piece, can I cut off a small piece for my tight application without destroying it??…should I compress it before cutting, so it will expand when I pull it out for cleaning?

  19. Reuben Saltzman
    July 14, 2013, 12:51 pm

    Bill – I have a similar setup at my own house, and I just push by dryer right up against the rigid duct. Is that possible for you? If not, it’s easy to cut Dryerflex. Use the shortest amount that you can.

  20. Bill White
    July 14, 2013, 3:51 pm

    I will try that…Do you know the dimension for the Dryerflex fully compressed 48 inch duct…from the literature it appears that the package as shipped is about 12 inches high….that will be to big for my space and I will have to cut it back…

  21. Reuben Saltzman
    July 14, 2013, 7:37 pm

    I’d guess the Dryerflex compresses to about 6″.

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