Reuben's Home Inspection Blog


Dryer Transition Ducts, Lint, and Fires

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.

Reuben Saltzman, Structure Tech Home Inspections


Comment balloon 44 commentsReuben Saltzman • August 14 2012 05:14AM


Great post.  I think I will be forwarding people to this.

Posted by Gary Pike (Better Homes and Gardens Real Estate Metro Brokers) almost 7 years ago

Thanks Gary.

Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) almost 7 years ago

Great info - I can't wait to see what you think of DryerFlex

Posted by Kathleen M. Feeney, Mt. Kisco Real Estate - EcoBroker (Cafe Realty) almost 7 years ago

I knew this would get featured before I got to push the button:)  Maybe we should start running b-vent and flex b-vent for these installations :)

Posted by Charles Buell, Seattle Home Inspector (Charles Buell Inspections Inc.) almost 7 years ago

Great post and excellent advice. I actually saw an electrical spark from a short, burn a one inch hole right through a brand new, semi-ridged metal duct. 

Posted by Dennis J. Zisa & Associates, Inc., 28 years in So. Jersey and the Greater Camden area (Dennis J. Zisa & Associates, Inc.) almost 7 years ago

A real common problem here.  I look forward to your next test with Dryerflex.

Posted by Anonymous almost 7 years ago

Very good information and the visuals should really sink in with those people who are visual.

Posted by Than Maynard, Broker - Licensed to List & Sell - 405-990-8862 (Coldwell Banker Heart of Oklahoma) almost 7 years ago

What an important tip! Thank you so much Reuben.

Posted by Vanessa Saunders, From Manhattan to the Catskills of New York (Global Property Systems Real Estate) almost 7 years ago

Great reminder to all of us to check out what we have and replace when necessary.

Posted by Nan Jester, Realtor, Exit Real Estate Gallery (Exit Real Estate Gallery Jacksonville Beach, FL ) almost 7 years ago


Yikes! I have the plastic transition duct connected to my dryer.  Now what do I do?  You have scared me but haven't offered a viable option.  Help.

Posted by Evelyn Kennedy, Alameda, Real Estate, Alameda, CA (Alain Pinel Realtors) almost 7 years ago

Reuben, You may have saved someone's life posting this great information. You just never know.


Posted by Debbie Reynolds, Your Dedicated Clarksville TN Real Estate Agent (Platinum Properties) almost 7 years ago

Great follow-up post Reubs.  You are a regular mad scientist!

Good thing you had that childhood so full of lighting fires...

That's it, isn't it?

Posted by Jay Markanich, Home Inspector - servicing all Northern Virginia (Jay Markanich Real Estate Inspections, LLC) almost 7 years ago

I did not know they had to be stretched tight and not smashed.  I have mine lined up with the hole and then smashed tight against it so the dryer doesn't stick out in the room so far.

Posted by Chris and Dick Dovorany, Broker/Associate at Premiere Plus Realty ( Homes for Sale in Naples, Bonita Springs and Estero, Florida) almost 7 years ago

Dryer ducts must be checked periodically to avoid fire hazards

Posted by Harry F. D'Elia, Investor , Mentor, GRI, Radio, CIPS, REOs, ABR (Real Estate and Beyond, LLC) almost 7 years ago

Like the shirt. Looking to start your own version of the show? Interesting results and a great job with the post. Looks like you had some fun with this one. 

Posted by James Quarello, Connecticut Home Inspector (JRV Home Inspection Services, LLC) almost 7 years ago

Reuben...great information, thanks for sharing with folks!  My daughter had the plastic duct as recent as a week ago, which by the way started a fire.  The dryer backs up to her bedroom, luckily the fire started during the day.  I'm quite sure it scared her enough that she'll never go to bed again with the dryer running, ever again.


Run, don't walk and get those plastic ducts changed out.

Posted by Wayne Bennett, Real Estate...As It Should Be (One Home Team Realty/Charlotte,NC 704-293-3931) almost 7 years ago

What a great post! I love your videos...

Thanks for sharing.

Posted by Tatyana Makarov, Your Greater Hartford Area Realtor (Coldwell Banker Residential Brokerage) almost 7 years ago

When I see the plastic or foil type duct I always write it up as a defet and recommend that it be replaced with one that is listed.  I like the sound of the Dryer flex.  Thanks for the link.


Posted by Robert Sole (REM Inspections LLC) almost 7 years ago

Yeah, This is great, I say GREAT information.  About two or three weeks ago, I posted a short blog about dryer fires.  Only because we woke up that Sunday morning to our neighbor's dryer fire.  Took out a garage, a car, and most of the front of the house.  Firefighters said it had been mickey-moused.

Posted by Anonymous almost 7 years ago
Wow that is some good information. That stuffed duct was a complete fire hazard.
Posted by Kevin Mackessy, Dedicated. Qualified. Local. (Blue Olive Properties, LLC) almost 7 years ago

I know these plastic ducts are not going to pass a goood inspectors eye and I have muy clients replace them before we get to the inspection.

Posted by William Feela, Realtor, Whispering Pines Realty 651-674-5999 No. (WHISPERING PINES REALTY) almost 7 years ago

Kathy - I think I'll have some info on the DryerFlex products sooner than I thought.

Charles - you know, that wouldn't be a bad idea.  The UL listed semi-rigid duct felt pretty similar to a flexible B-vent.

Dennis - I can see it happening very easily.

Than - thanks, the visuals certainly worked for me :)

Vanessa - thanks for reading. 


Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) almost 7 years ago

Nan - exactly.  This is fairly simple DIY stuff.

Evelyn - if you can replace the dryer transition duct with all metal duct material, that would be best.  If it's too difficult to get behind your dryer with a rigid duct, your next best option would be to use a UL listed semi-rigid duct.  For instance, try the one I linked to above. .  

Debbie - or at least helped to prevent some property damage :)

Jay - Oh man, you know it.  I spent a lot of time doing stuff like this just for fun... not that this wasn't fun.

Chris and Dick - it's high time to fix that.

Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) almost 7 years ago

Harry - you got it.

James - you noticed (insert bashful emoticon)!  Yeah, working on Mythbusters would certainly be my dream job.  In the meantime, I'll have to be happy with these low-budget experiments.

Wayne - thanks for sharing your story.

Tatyana - thanks, they were fun to make.

Robert - I'm not nearly as critical of the foil ducts, but there seems to be an older version of the foil that actually *is* flammable.  I think I need to do a little more investigation in to that matter.

Kevin - just think about how long it must have taken those people with the stuffed duct to get their clothes dry!

William - that's excellent advice for your clients.


Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) almost 7 years ago

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

Posted by Marshall Brown, BSEE, CHI (Mid America Inspection Services, LLC) almost 7 years ago
Great info!
Posted by Kathy McAlpin (HomeSmart - Arrowhead) almost 7 years ago

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!

Posted by Travis "the SOLD man" Parker; Associate Broker, email: / cell: 334-494-7846 (Team Linda Simmons, Enterprise, AL 36330) almost 7 years ago

Thanks for the information.  Scary.

Posted by Gail Fabiani (Right at Home Realty Inc., Brokerage) almost 7 years ago

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.

Posted by Michael J. O'Connor, Eastvale - 951-847-4883 (Diamond Ridge Realty) almost 7 years ago

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

Posted by Bob Miller, The Ocala Dream Team (Keller Williams Cornerstone Realty) almost 7 years ago

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.  

Posted by Christie Lane Craven, Your Anne Arundel County Agent (Blackwell Real Estate ) almost 7 years ago

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!

Posted by Jay Markanich, Home Inspector - servicing all Northern Virginia (Jay Markanich Real Estate Inspections, LLC) almost 7 years ago

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.

Posted by Rob Ernst, Reno, NV-775-410-4286 Inspector & Energy Auditor (Certified Structure Inspector) almost 7 years ago

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

Posted by Mary Hutchison, SRES, ABR, Experienced Agent in Kansas City Metro area (Better Homes and Gardens Real Estate-Kansas City Homes) almost 7 years ago

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.


Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) almost 7 years ago

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.

Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) almost 7 years ago

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

Posted by Carla Freund, Raleigh - Cary Triangle Real Estate 919-602-8489 (Keller Williams Preferred Realty) almost 7 years ago





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

Posted by John DL Arendsen, Crest Backyard Homes "ADU" dealer & Contractor (CREST BACKYARD HOMES, ON THE LEVEL GENERAL & FACTORY BUILT HOME CONTRACTOR, TAG REAL ESTATE SALES & INVESTMENTS) almost 7 years ago

Carla - it's easy to just forget about.

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

Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) almost 7 years ago

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.

Posted by Donald Hester, NCW Home Inspections, LLC (NCW Home Inspections, LLC) over 6 years ago

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

Posted by Wayne B. Pruner, Tigard Oregon Homes for Sale, Realtor, GRI (Oregon First) over 6 years ago

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 

Posted by Clint Mckie, Desert Sun Home, Comm. Inspection 1-575-706-5586 (Desert Sun Home, commercial Inspections) over 6 years ago


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

Posted by Wallace S. Gibson, CPM, LandlordWhisperer (Gibson Management Group, Ltd.) over 6 years ago

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

Posted by Charles Stallions Real Estate Services, Buyers Agent 800-309-3414 Pace and Gulf Breeze,Fl. (Charles Stallions Real Estate Services Inc) over 6 years ago