Dryer Transition Ducts, Lint, and Fires

By
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.

Conclusions

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.

close

Re-Bloggged 3 times:

Re-Blogged By Re-Blogged At
  1. Evelyn Kennedy 08/14/2012 10:01 AM
  2. Winston Heverly 01/05/2013 05:02 AM
  3. David Popoff 01/05/2013 06:29 AM
Spam prevention

Accessibility option: listen to a question and answer it!

To submit the form,
drag the car to the circle on the side.

Type below the answer to what you hear. Numbers or words, lowercase:

Topic:
Home Improvement
Groups:
Home Inspector's Corner
Ask the Home Inspector
ASHI
Minnesota Real Estate Investor Group
Minnesota Real Estate
Tags:
drye
ul listed
ul listed semirigid dryer duct
foil dryer ducts
clothes dryer transition ducts
transition ducts
dryer transition ducts

Comments 44 New Comment

Anonymous
Post a Comment
Spam prevention

Accessibility option: listen to a question and answer it!

To submit the form,
drag the tshirt to the circle on the side.

Type below the answer to what you hear. Numbers or words, lowercase:

Rainmaker
341,793
Donald Hester
NCW Home Inspections, LLC
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.

August 21, 2012 11:13 PM
Rainmaker
260,368
Wayne B. Pruner
Tigard Oregon Homes for Sale, Realtor, GRI
Oregon First

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

November 13, 2012 07:38 PM
Rainmaker
689,174
Clint Mckie
Desert Sun Home, Comm. Inspection 1-575-706-5586
Desert Sun Home, commercial Inspections

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 

January 05, 2013 06:36 AM
Rainmaker
1,056,080
Wallace S. Gibson, CPM
LandlordWhisperer
Gibson Management Group, Ltd.

 

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

 
January 06, 2013 02:11 AM
Rainmaker
813,159
Joyce Kelley
Buyers Agent 800-309-3414 Pace and Gulf Breeze,Fl.
Charles Stallions Real Estate Services Inc

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

January 07, 2013 09:12 AM
Anonymous
Post a Comment
Spam prevention

Accessibility option: listen to a question and answer it!

To submit the form,
drag the magnifying-glass to the circle on the side.

Type below the answer to what you hear. Numbers or words, lowercase:

Rainmaker
229,341

Reuben Saltzman

Minneapolis Home Inspections
Ask me a question
*
*
*
Spam prevention

Accessibility option: listen to a question and answer it!

To submit the form,
drag the key to the circle on the side.

Type below the answer to what you hear. Numbers or words, lowercase:

Additional Information

Home inspection topics in the Minneapolis / Saint Paul area.