Dryer Venting

By Frank G. Ross

A home’s dryer vent is critical to the safe and efficient operation of the dryer.  The clothes dryer is one of the most expensive appliances in the home.  The longer it runs, the more money it costs. Improper venting leads to lint build-up which restricts air flow causing the dryer to work harder and longer.  It also leaves the home at risk of a fire.  Two main factors are the source of most improperly vented dryers – the composition and the configuration of the duct.

Composition refers to the material of which the duct is made.  Rigid, smooth-walled ducting should be a homeowner’s first choice, and it should be assembled using metal foil tape and not screws or rivets because they project into the interior of the duct and catch lint.  Duct tape should not be used either because it will deteriorate with time.  The American Household Appliance Manufacturers Association (AHAM) recommends the use of either rigid aluminum or steel duct or spiral-wound aluminum flex hose with a 4 inch diameter--NOT the white vinyl hose. 

I have often seen white vinyl hose, corrugated dryer ducting or plastic pipe used to vent a dryer.  None of these are UL approved and constitute a fire hazard.

The configuration of a duct describes the pathway that the duct follows from the dryer to the exterior of the home.   As a general rule duct runs should be kept as straight as possible and should be well supported.  Ninety degree turns or other sharp turns cause more back pressure creating resistance to air flow and making it easier for lint to accumulate.  Two 45 degree turns are more efficient than one 90 degree turn.  Specific guidelines on the recommended length of the duct are also available.

Lint accumulation in any quantity not only shortens the life of the dryer, but it is also a fire hazard. Over 13,000 house fires per year are reported to start in or around the dryer.

Another often overlooked aspect of dryer vents is the location of the discharge.  The duct must vent to the outdoors, not to a crawlspace, attic, basement, garage, or interior vent kit.  When clothes are dried a large volume of warm, moist air is discharged.  Allowing the dryer to vent somewhere inside the structure increases the humidity in the home.  This trapped moisture can cause problems with wood rot and mildew growth. 

In more than one home I have inspected I have observed a flexible duct with a nylon stocking over the end of it venting into a room for extra heat. Again, that is unacceptable due to the lint build-up in the hose and the excess moisture.

The exterior wall dampers should have a hood and/or functioning flaps to keep out the weather.  Also, they should not be located in a window well or near a gas vent or chimney.  A larger opening is preferable because it allows for greater airflow.  A screen or any such covering is not recommended since it would tend to restrict airflow and collect lint.

For homeowners, some indications that there might be a problem with the dryer venting include long drying times, the dryer overheating, or the dryer smelling hot during use.

Here is another item homeowners can add to their seasonal maintenance checklist.  Using a vent brush, clean out the dryer vent at least once a year.  Remove any accumulated lint.  Be sure the exterior vent flap opens and closes freely.  Consider replacing any crushed or improper ducts.

Frank Ross is a Certified Utah Home Inspector for Pillar to Post Professional Home Inspection and a full member of the National Association of Certified Home Inspectors and a member in good standing with the Utah Better Business Bureau.  Readers may contact Mr. Ross at (435) 867-6400 or frank.ross@pillartopost.com