Clothes dryers, lint, and fires

Home Inspector with Structure Tech Home Inspections

According to Underwriters Laboratories, clothes dryers are responsible for approximately 15,000 home fires each year.    It's not hard to believe.  Improperly installed and improperly maintained clothes dryer ducts are one of the most common issues that home inspectors find, but it's not that difficult to keep your clothes dryer safe.  Today I'll discuss dryer duct installations and maintenance.


In Minnesota, the installation requirements for clothes dryer ducts can be found in Section 504 of the Minnesota Mechanical Code.   I won't go over all of the requirements, but I will mention a few of the items that most people have questions about.

Dryer duct length - the maximum allowable length for a clothes dryer duct is 25'.  Each 90 degree turn in the duct is worth 5', and each 45 degree turn is worth 2.5 feet.  For a typical basement in Minneapolis or Saint Paul, the clothes dryer has a 90 degree turn in the duct right behind the dryer, then another 90 degree turn at the ceiling.  Assuming it's a 7' ceiling, this leaves 8' of run before the dryer duct needs to terminate at the exterior, according to these requirements.

While many clothes dryers have a longer run than this, it's not always a problem.   There's an exception to the rule which says "where the make and model of the clothes dryer to be installed is known and the manufacturer's installation instructions for such dryer are provided to the code official, the maximum length of the exhaust duct, including any transition duct, shall be permitted to be in accordance with the dryer manufacturer's installation instructions.".  

In other words, if the dryer manufacturer allows a longer duct, no problem.

I've read a lot of dryer installation manuals, and in every case the dryer manufacturer allowed for a much longer run than what's allowed by code; for instance, a 29" Maytag clothes dryer allows for a 100' duct when two elbows are used.

I once inspected a condo conversion building in Saint Louis Park where the contractor had attached a placard to the location where the dryer would go, warning that the maximum length of the drier (sic) vent was limited to 30' with three elbows.

Dryer vent placard

Dryer duct construction - dryer ducts need to vent to the exterior, be made from metal, be at least 4" in diameter, and have a smooth interior.  The entire duct needs to be supported and secured, and no screws are allowed on the joints because they could accumulate lint.  Flexible materials, such as foil, plastic, and semi-rigid metal aren't allowed.  Those are all common materials used for a dryer transition duct - the material that can be used to get from the dryer to the duct.

Dryer transition duct

The terminal for the dryer needs to have a backdraft damper, and no screens are allowed at the dryer exhaust.  When screens are installed, they get clogged with lint.  This reduces the performance of the dryer and creates a potential fire hazard.

Clogged dryer duct

I've heard concerns about pests getting in to the clothes dryer duct if a screen isn't installed, but if the backdraft damper at the exterior is kept clean, this shouldn't be an issue.

Transition Ducts are a big enough topic to deserve their own post.  I'll write about these next week.

Clothes Dryer Maintenance

Clothes dryer maintenance is actually quite simple: keep it clean.  Dryer lint is flammable, and the more that accumulates in the dryer and the duct, the greater the risk.  The most obvious and routine part of this is keeping the lint screen clean - it should be cleaned after every load.

Periodically check the damper at the exterior to make sure it's clean; when lint accumulates at the damper it will eventually cause the damper to stay open.

Dirty dryer terminal

If you're unfortunate enough to have a dryer that exhausts through the roof... I'm sorry to hear it.  Someone needs to get up there on a regular basis to clean the damper.

If you have a dryer duct that passes through a concealed or infrequently visited space, such as an attic or crawl space, you should check on it periodically to make sure that everything is still properly connected.  A disconnected clothes dryer duct will exhaust a ridiculous amount of lint and moisture in to the home.

Disconnected dryer duct in crawl space

Take a peek behind your dryer with a flashlight periodically - it's quite common for the dryer to come disconnected from the duct, which makes a big mess of flammable lint behind the dryer.  The dryer duct itself needs to be cleaned periodically as well.  You can find instructions for cleaning your own dryer duct here -  This sounds like a good project for the next rainy weekend.

I'll have plenty more to discuss next week on the topic of clothes dryer transition ducts.

Comments (44)

Barb Merrill
Cactus Mountain Properties, LLC - Tempe, AZ
GRI, Associate Broker

Thank you for drawing awareness to this potential disaster.  I know because I had a dryer fire.  Thank heavens I was home and caught it right away.  I learned you should routinely wash your lint trap with soap and water to prevent build-up.  I'm going to pull mine out right now and give it a good scrubbing!

Aug 07, 2012 06:05 AM
Tatyana Makarov
Coldwell Banker Residential Brokerage - South Windsor, CT
Your Greater Hartford Area Realtor

Wow, what a "beautiful" photos! thank you for the post. During home inspections I've seen it all :)

Aug 07, 2012 07:09 AM
Robert L. Brown - Grand Rapids, MI
Grand Rapids Real Estate Bellabay Realty, West Mic

I've seen some funky ones out there. People need to stay up on this.

Aug 07, 2012 07:19 AM
William Feela
Realtor, Whispering Pines Realty 651-674-5999 No.

And I thought most of these installation directions were just suggestions.

Aug 07, 2012 09:42 AM
Sharon Alters
Coldwell Banker Vanguard Realty - 904-673-2308 - Fleming Island, FL
Realtor - Homes for Sale Fleming Island FL

Reuben, the photos are so graphic - the one with the grid reminds me of the dust that gets on my blow dryer and ruins them. Ours vents through the roof - guess Frank has a task to do :)


Aug 07, 2012 12:05 PM
Mel Ahrens, MBA, Kelly Right Real Estate
Kelly Right Real Estate - Hood River, OR
Customized Choices for your Real Estate Needs

Thanks for the reminder of this important/dangerous issue. We had a dryer vent fire once, but luckily we were home and once I smelled smoke and turned the dryer off, the fire went out on its own. It would have been a very different story if I hadn't been right there.


Aug 07, 2012 01:17 PM
Rob Ernst
Certified Structure Inspector - Reno, NV
Reno, NV-775-410-4286 Inspector & Energy Auditor

I think the duct should be insulated when it passes through cold spaces. The hot damp lint is just looking for a cold pipe to stick to.

Aug 07, 2012 02:12 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.

Having seen the effects of this first hand I have learned what you are teaching. One of the most dangerous situations in a home.

Aug 07, 2012 02:36 PM
Sharon Parisi
United Real Estate Dallas - Dallas, TX
Dallas Homes

Reuben, your photos are graphic!  I am fortunate that my vent line is about 3 feet.  As a Realtor I have seen everything!

Aug 08, 2012 07:12 AM
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Aug 10, 2012 03:24 PM
Reuben Saltzman
Structure Tech Home Inspections - Minneapolis, MN
Delivering the Unbiased Truth.

Wallace - great idea.  You'll improve the performance of the dryers as well.

Jeffrey - crazy, huh?

Jay - no doubt.  I had a family member complain about their clothes dryer taking forever to dry the clothes... and I found a gigantic chunk of lint completely blocking the dryer exhaust at the exterior.  Bad times.

Jared - thanks.

Janis - check your manual though.  Allowable lengths vary.

Aug 10, 2012 10:16 PM
Reuben Saltzman
Structure Tech Home Inspections - Minneapolis, MN
Delivering the Unbiased Truth.

Scott S - wow, and right next to your house?  Scary stuff.  Did you ever find out what caused the dryer duct fire?

Richie - just like the bug zapper?  That would be cool.

Robert - I bet!  It's even better than paper. 

Chris - say it ain't so ;)

Susan - I've seen a ton of houses with screens over the dryer ducts that were installed by exterminators.  Bad news.  

Aug 10, 2012 10:25 PM
Reuben Saltzman
Structure Tech Home Inspections - Minneapolis, MN
Delivering the Unbiased Truth.

Athina - definitely.  I've been in some rental properties where the landlords have put up big notices by the dryers reminding the occupants to clean the lint screens after every load.

Chris and Dick - it sounds like you shouldn't have much to worry about :)

John- good stuff.

Beth - I'll have a follow up to this on Tuesday as well.

David - exactly.

Aug 10, 2012 10:30 PM
Reuben Saltzman
Structure Tech Home Inspections - Minneapolis, MN
Delivering the Unbiased Truth.

JudyAnn- that's a great idea!  I might have to start saving my dryer lint and toilet rolls for that purpose.

Robert - I've noticed.  Even though the foil transition ducts are UL Listed, many AHJs in my area won't allow them.

Morris - I especially wonder what people where thinking when the exhaust terminals are located on steep two-story roofs.  I know plenty of home inspectors who don't even get on those.

Sandy - all the more reason to make sure it's maintained properly.

Barb - I've never heard of the soap and water thing, but it couldn't hurt.  My little trick is whenever I have my wet/dry vac out and I'm using it near the laundry room, I vacuum down my dryer lint screen.  Seems to do a pretty good job.

Aug 10, 2012 10:36 PM
Reuben Saltzman
Structure Tech Home Inspections - Minneapolis, MN
Delivering the Unbiased Truth.

Tatyana - I'll have some even better photos next week :)

Robert - correct.  This is important stuff.

William - ha!  :)

Sharon - I know exactly what you mean with the hair dryer.  I've cleaned my wife's...

Gretchen- good catch!  The video Scott posted in comment #10 might be a good example of what could have been.

Aug 10, 2012 10:40 PM
Reuben Saltzman
Structure Tech Home Inspections - Minneapolis, MN
Delivering the Unbiased Truth.

Rob - definitely.  If it's not insulated, you'll get plenty of condensation inside the duct.  Here in MN, the last 3' of the duct also needs to be insulated before it gets to an unconditioned space.

Joyce - and clothes dryers seem so innocuous...

Sharon - that's a nice length :).  Short and sweet.

Aug 10, 2012 10:43 PM
James Quarello
JRV Home Inspection Services, LLC - Wallingford, CT
Connecticut Home Inspector

I've found disconnected ducts in attics and crawl spaces. It does make the place smell good :)

Aug 10, 2012 11:14 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.

Such a good post and lots to take heed to. We never think of these things till perhaps it is too late

Aug 13, 2012 01:05 PM
Scott Seaton Jr. Bourbonnais Kankakee IL Home Inspector
SLS Home Inspections-Bradley Bourbonnais Kankakee Manteno - Bourbonnais, IL
The Home Inspector With a Heart!

Reuben, the dryer fire started with a stuffed lint trap, in the dryer, went thru the vent up the wall and into the daughter's bedroom, then thru the walls into the attic. First responder showed up with a fire extinguisher. They were home and got out safely. 

Aug 14, 2012 09:41 PM
Donald Hester
NCW Home Inspections, LLC - Wenatchee, WA
NCW Home Inspections, LLC

Reuben, Good stuff as always. Love the lint forest pictures. I had one just a couple of weeks ago.

Aug 21, 2012 04:23 PM