Dryer Vent Safety & Maintenance

by Scott Brown – 1/7/20

Every single year there are 15,000 house fires caused by clothes dryers according to the National Fire Protection Association.

Why do most dryer fires occur? Lack of maintenance and improper installation.

dryer fire

The lint that is produced from drying clothes is highly flammable. When it gets trapped in the dryer vent it blocks the vent and becomes a fire hazard.

Dryer Vent Installation

Dryer vents have three sections. The transition duct and the exhaust duct at the interior, and the dryer vent cover at the exterior. These three sections create what is commonly known as the dryer vent.

dryer vent
dryer vent cover open 1 Edited - Dryer Vent Safety & Maintenance

The Dryer Exhaust Duct

The exhaust duct is the portion of the vent that penetrates the wall and goes outside. It also connects to the transition duct when there is one.

The International Residential Code (IRC) says the exhaust duct should meet the following standards:

  • be composed of rigid metal
  • have a 4 inch diameter
  • have a smooth interior finish.

The IRC also states the maximum length of the exhaust duct should be 35 ft. That length is also reduced 5 ft for every 90 degree angle and 2.5 ft for every 45 degree angle.

The IRC also gives manufacturers leeway to override the 35 ft maximum length and most do. Powered vents are also an option when the vent needs to run for an extended length.

Some GE models are approved to have over 100 ft of exhaust duct, unfortunately there is no standard. Additionally the length of the exhaust duct is measured from dryer vent hood to the transition duct connection, so you can ignore the transition ducts length in this calculation. Check out this chart to see maximum lengths for several manufacturers:

exhaust duct length chart


The Dryer Transition Duct

The transition duct is the portion of the vent that connects to the dryer.

Here is what the IRC says regarding the transition duct.

  • It should be Underwriters Labroatory (UL) approved, look for the logo on the packaging
  • It should be a maximum length of 8ft
  • It should not pentrate walls, even an an interior wall
  • It should be attached without screws as they catch lint. Use metal HVAC tape and/or a hose clamp to connect sections of duct

Importantly there also some material requirements.

First and foremost vinyl or plastic ducts are not acceptable. Chuck those right in the trash.

Rigid sheet metal is allowed, semi-rigid metal is allowed, and metal foil is allowed; although with a number of caveats as some manufacturers don’t want it used, so it’s best just to ignore it.

dryer vent types

So the transition duct can be made of the same rigid sheet metal as the exhaust duct?

Yes, it can. This sounds like a great solution,and on paper it is. In practice this doesn’t allow for movement of the dryer and creates a hassle during maintenance and cleaning.

The transition duct is an area that is prone to lint buildup when there are problems. Crushed or damaged duct should be replaced as it reduces airflow and allows lint to get hung up in the vent..

damaged dryer vent

Crushed transition duct should be replaced

Semi-rigid is the best option for  most situations for its durability and ability to flex, which makes it easy to use. Some folks are convinced that DryerFlex is the bet option available.

You can check out DryerFlex here, private labeled for GE.

The Dryer Vent Cover (aka Dryer Hood)

The purpose of the vent cover to prevent drafts and critters from entering through the dryer vent. To accomplish this the vent cover should have a back-draft damper. Essentially a hinged or slotted cover that opens when the dryer blows air through the vent.


Did you catch that?

One more time for everybody in the back…

Dryer vent covers, the outside part of the vent, should never have screens or cages of any kind. They are excellent at trapping lint and creating fire hazard conditions. This is one of the most common problems home inspectors see with dryer installations.

dryer vent cover closed

A proper dryer vent cover

Dryer Maintenance

Dryers should be maintained regularly to prevent unsafe conditions.

  • Lint traps in the unit should be cleaned after every use
  • Check the vent cover every few months to make sure it is free of blockage, clean out any lint
  • Remove and clean (or replace) your vents exhaust duct and transition duct annually

Even properly installed dryer vents, when not cleaned regularly can end up looking like this:

blocked dryer vent

Legal Stuff: Any references to code are to IRC. Check with your jurisdiction to see local regulations which may differ. Homeowners should never perform repairs or maintenance that they are unqualified to perform, and should consider when they may be putting the safety of themselves or others at risk.

Scott - Brightside Home Inspections - headshotScott Brown is a New York state licensed home inspector. He is an alumnus of Syracuse University and has worked in the construction/inspection industry for more than 10 years. He grew up working on remodeling projects around the house with his dad, much to his displeasure at the time. Scott is the owner of Brightside Home Inspections in Syracuse, NY.