Reuben's Home Inspection Blog

head_left_image

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

I've always told my Minnesota home inspection 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-rigidmaterial 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

        

Comment balloon 13 commentsReuben Saltzman • April 13 2010 05:18AM

Comments

Thanks for sharing this important information with us this morning. Great stuff

Posted by Harry F. D'Elia, Investor , Mentor, GRI, Radio, CIPS, REOs, ABR (Real Estate and Beyond, LLC) over 8 years ago

Reuben I think the corrugated stuff has too many "nooks and crannies."  The think about the flexible foil duct is that while it has a UL listing as a "transition" duct material, most manufacturer's installation instructions prohibit its use.  Looks like we are back to rigid metal pipe :)

Posted by Charles Buell, Seattle Home Inspector (Charles Buell Inspections Inc.) over 8 years ago

ATCO makes a UL listed Semi-rigid aluminum duct. Most building inspectors will not pass the foil type dryer vent even though they are UL listed and they will pass the Semi-rigid type even though it is not UL listed. It is like the plastic discharge line from the pressure relief valve for a water heater that is UL listed but no building inspector will pass them. 

Posted by Andy over 8 years ago

Hi Harry, thanks for reading.

Charles - that's a good theory.  Most manufacturers prohibit the foil stuff?  I'll have to read through a few more manuals.  I've never seen that - thanks for the tip.

Andy - I found a UL listed semi-rigid aluminum duct at the ATCO web site, but it's only listed for furnace ductwork.  You're exactly right about about the water heater discharge pipes!

Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) over 8 years ago

I always recommend a smooth walled duct for dryers.

Posted by Vince Santos, Southeast Michigan Home Inspector (StepByStep Home Services LC) over 8 years ago

Vince - that's solid advice.  

Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) over 8 years ago

The foils have too many lint catchers inside.  The semi-rigid is much smoother.  Why it isn't listed is beyond me...

Posted by Jay Markanich, Home Inspector - servicing all Northern Virginia (Jay Markanich Real Estate Inspections, LLC) over 8 years ago

Jay - the best reason I've heard is that the semi-rigid stuff won't spring back to it's original shape after it gets bent.  That's a good point.

Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) over 8 years ago

It also splits easily.  But hey, no cloggo.

Posted by Jay Markanich, Home Inspector - servicing all Northern Virginia (Jay Markanich Real Estate Inspections, LLC) over 8 years ago

Thanks for pointing that out.  Interesting stuff always comes up here.

Posted by Gene Allen, Realty Consultant for Cary Real Estate (Fathom Realty) over 8 years ago

What the.......Wow, Thanks for the research Rubin.  I need to keep on top of your posts, I might learn a thing or two!

Posted by Jim Allhiser, Salem, Oregon Home Inspector (Perfection Inspection, Inc.) over 8 years ago

Good information, Reuben.  Thanks for sharing.  Have a great week.

Eldon

Posted by Eldon Hendrix (Hendrix and sons Home Inspections) almost 8 years ago

Thanks for reading, Eldon.

Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) almost 8 years ago

Participate