Dryer Transition Ducts, Lint, and Fires

Home Inspector with Structure Tech Home Inspections

Last week I blogged about clothes dryer ducts, and this week I'm going to follow up with information on dryer transition ducts.  As I mentioned last week, a dryer transition duct is the flexible material that can be used to transition between the dryer and the duct.  Transition ducts should be used sparingly, stretched tight, not smashed, and replaced periodically.    They're allowed by the Minnesota State Mechanical Code, but they can't be any longer than 8', and they need to be listed and labeled for the application.  The key word is listed.   If a dryer transition duct is listed, you'll find the "UL" logo somewhere on the package or product.

Today I'll discuss the three most common materials used for dryer transition ducts, and I'll cover some basic rules for keeping your dryer transition duct safe.

Plastic Ducts

Plastic dryer transition ducts are a potential fire hazard.  They're never UL listed, they can get clogged with lint, and they'll burn.  If you have one of these, replace it.  I looked for one of these at Home Depot and Menards, but I couldn't find one.  Good.  I still find plenty of them while inspecting houses though.

Clogged Dryer Duct

I tried lighting some paper on fire inside one of these plastic ducts to see how fast it would burn through, and the plastic itself actually caught on fire.


Foil Ducts

Foil dryer transition ducts are typically UL Listed, and they're readily available at any home improvement store.  While these products are allowed by code, I've heard that many municipal inspectors won't allow them, and most manufacturers of clothes dryers don't recommend them either.

Foil Duct

I tried burning one of the UL Listed foil ducts by filling it up with shredded paper, then lighting the paper.  Once the paper caught fire, I accelerated the burn by aiming the blower end of a wet/dry vac at the tube.  Some people claim that these foil ducts are flammable, but that's not true; there are two versions of the foil dryer transition ducts - a listed and a non-listed version.  That's the listed version shown in the photo below.  After heavy white smoke started pouring out the end, it took about 10 seconds for the flames to rip through the side.

UL Listed Foil Duct

Semi-Rigid Metal Ducts

Semi-rigid metal dryer transition ducts are available anywhere dryer duct materials are sold, but it's almost impossible to find a UL Listed version of this.  The strange thing is that these semi-rigid ducts seem to be universally accepted by building code officials, and they're recommended by clothes dryer manufacturers.  Everyone seems to like these, but they have their drawbacks: they puncture easily, they crush easily, they unravel easily, and they have very sharp edges.  I repeat, very sharp edges.

After a ton of searching at local retailers and searching online, I couldn't find a single UL Listed semi-rigid duct, so I concluded there was no such thing as a UL Listed semi-rigid metal duct.

But there is.

I sent out emails to several major clothes dryer manufacturers, asking what consumers are supposed to use for a dryer transition duct, because there doesn't seem to be a UL listed semi-rigid duct.  Finally, a very helpful person at Whirlpool by the name of Lee Herendeen sent me a link to just such a product, made by Lambro Industries, Inc.  After all the searching I had been doing, I was skeptical that this was the real thing, so I ordered one.  It's the real thing.

The photo below shows the UL listed semi-rigid duct from Lambro sitting next to a non-listed duct.

Listed vs non-listed duct

The UL listed duct was much stiffer than the non-listed duct, and was much more difficult to crush.   To continue my comparison of transition ducts, I stuffed them both full of shredded paper, lit the paper on fire, then aimed the exhaust from a wet/dry vac in to the duct to simulate the air from a clothes dryer.

I started with the non-listed duct.

At about the 40 second mark, heavy smoke started to come out the back side of the duct.  About 17 seconds later the fire burned through the duct.

The next test was to try the same thing with the UL Listed duct.

With this one, heavy smoke started coming out at about the 30 second mark, and it took about 27 seconds for the fire to burn through the duct.  Of course these aren't 'real life' tests of a dryer duct fire, but it's interesting to compare the performance of the different materials.


Don't use plastic for your dryer duct.  It's flammable.

Foil comes in a UL Listed flavor and is easy to work with, but it's prohibited by many building code officials and clothes dryer manufacturers.

Semi-rigid aluminum is good, but it's a hassle to work with.  If you're going to use semi-rigid, use the UL listed version.

Next year I might check out a product called DryerFlex.  They claim their product offers the best of both worlds.  We'll see.

Comments (44)

Marshall Brown
Mid America Inspection Services, LLC - Fargo, ND

I came away after reading this feeling like I had learned something in sufficient depth to really explain it to a client. Thanks!

Aug 14, 2012 10:31 PM
Kathy McAlpin
HomeSmart - Arrowhead - Peoria, AZ
Great info!
Aug 14, 2012 11:03 PM
Travis "the SOLD man" Parker; Broker/Owner
Travis Realty - Enterprise, AL
email: Travis@theSOLDman.me / cell: 334-494-7846

I sorta remember seeing the plastic, but it's been awhile. Plus, I generally (uh, like really NEVER) go around looking behind people's dryers. But haven't seen them in a loooooong time, when I actually would see behind a dryer....

EXCELLENT info & demo!

Aug 14, 2012 11:15 PM
Gail Fabiani
Right at Home Realty Inc., Brokerage - Burlington, ON

Thanks for the information.  Scary.

Aug 15, 2012 12:52 AM
Michael J. O'Connor
Diamond Ridge Realty - Corona, CA
Eastvale - 951-847-4883

Thank you for a very informative post!  I know someone who nearly had a vent fire but I had no idea that there were different types of vents to review.  Sales in our area usually do not include the dryer but I can at least have an educated discussion now when the situation does come around.

Aug 15, 2012 01:27 AM
Bob Miller
Keller Williams Cornerstone Realty - Ocala, FL
The Ocala Dream Team

Hi Reuben, we agree.  It is said dryers are the number one source of house fires.

Aug 15, 2012 02:44 AM
Christie Lane Craven
Blackwell Real Estate - Odenton, MD
Your Anne Arundel County Agent

Reuben, I replace our current semi-rigid one with a new semi-rigid one about 6 months ago because it crushed and squished to oblivion.  Good thing they gave me a long piece of it because I ripped the first one trying to get the dryer back against the wall.  I can also attest to the fact that they are VERY sharp.  There was quite a bit of blood and profanity involved in the install.  

Aug 15, 2012 04:06 AM
Jay Markanich
Jay Markanich Real Estate Inspections, LLC - Bristow, VA
Home Inspector - servicing all Northern Virginia

I liked M-80s and cherry bombs!  We had fun with those and trash cans on peoples' porches!  Those were the days of the metal trash cans.  A cigarette on the fuse gave us a good five minutes to get away!

Aug 15, 2012 09:00 AM
Rob Ernst
Certified Structure Inspector - Reno, NV
Reno, NV-775-410-4286 Inspector & Energy Auditor

Nice experiments. Anytime you get to play with fire for research it's gonna be fun. The key is to keep that air flowing freely.

Aug 15, 2012 09:40 AM
Mary Hutchison, SRES, ABR
Better Homes and Gardens Real Estate-Kansas City Homes - Kansas City, MO
Experienced Agent in Kansas City Metro area

Thanks for the informative post and...looks like the research was a fun activity!  Will note for future home walk throughs!

Aug 16, 2012 03:14 AM
Reuben Saltzman
Structure Tech Home Inspections - Minneapolis, MN
Delivering the Unbiased Truth.

Marshall - Thanks, glad I could help!

Kathy - thanks.

Travis - It's crazy how many of those plastic ducts I still find... but of course, I always look behind the dryers.

Gail - definitely.

Michael - the bottom line is that the flexible stuff should be used sparingly.


Aug 16, 2012 11:38 AM
Reuben Saltzman
Structure Tech Home Inspections - Minneapolis, MN
Delivering the Unbiased Truth.

Bob - I believe it, and it's easy to understand why.

Christie  - you're not kidding about the blood and profanity.  Did you happen to notice that I was wearing a glove on my left hand in the second and third videos?  That was after slicing my thumb on that dang stuff.

Jay - I'm very jealous.  Growing up, I only got to hear about M-80s and cherry bombs.  Too many kids blew their hands up, apparently.  

Rob - it was fun :)

Mary - thanks for reading.  I'm going to have a follow-up post in the near future where I test out a few more materials.

Aug 16, 2012 11:43 AM
Carla Freund
Keller Williams Preferred Realty - Raleigh, NC
NC Real Estate Transition & Relocation 919-602-848

Reuben - Great Post! Many People don't take cleaning and caring for their dryer vents serious enough.

Aug 16, 2012 08:13 PM
John DL Arendsen
CREST "BACKYARD' HOMES, ON THE LEVEL General & Manufactured Home Contractor, TAG Real Estate Sales & Investments - Leucadia, CA
Crest Backyard Homes "ADU" dealer & RE Developer





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Ruben, Can I buy you one of these for future experiments? LOL!! Actually that's some very sobering information. Thanks!

Aug 17, 2012 12:39 AM
Reuben Saltzman
Structure Tech Home Inspections - Minneapolis, MN
Delivering the Unbiased Truth.

Carla - it's easy to just forget about.

John - Yes !  As I watched the videos I was thinking the same thing myself.  

Aug 17, 2012 09:49 PM
Donald Hester
NCW Home Inspections, LLC - Wenatchee, WA
NCW Home Inspections, LLC

Reuben, Heck if I knew you where going to have this much fun I would hung out a little longer to play ; ) I love this kind of stuff great vids.  Keep em coming they are really fun.

Aug 21, 2012 04:13 PM
Wayne B. Pruner
Oregon First - Tigard, OR
Tigard Oregon Homes for Sale, Realtor, GRI

I've just learned more about ducts than I ever thought possible.

Nov 13, 2012 11:38 AM
Clint Mckie
Desert Sun Home, commercial Inspections - Carlsbad, NM
Desert Sun Home, Comm. Inspection 1-575-706-5586

Hi Rueben,

Why is it no one cares about these issues till there is a fire in a home that's blamed on the dryer ducts catching fire?

It is a shame that more home owners don't read the posts we have on fires in the dryer ducts.

Have a great day and an even better weekend.

Best, Clint McKie 

Jan 04, 2013 10:36 PM
Wallace S. Gibson, CPM
Gibson Management Group, Ltd. - Charlottesville, VA


Fire safety is a concern for my residents 24/7....fortunately, my HVAC service firm tests smoke alarms and changes batteries twice annually 

Jan 05, 2013 06:11 PM
Charles Stallions Real Estate Services
Charles Stallions Real Estate Services Inc - Gulf Breeze, FL
Buyers Agent 800-309-3414 Pace and Gulf Breeze,Fl.

OMG I have not even thought about this, that is terrible. What build up?

Jan 07, 2013 01:12 AM