Armchair Builder

Clothes Dryer Exhaust Vent Design

A clothes dryer exhaust vent should be carefully designed into the architectural plans of a new home to prevent potential problems from occurring.  Some common problems with exhaust vents include rodent entry, lint buildup, cold air access, and potential fire hazards.  Let’s take a closer look at the dryer vent to help ensure a trouble free experience with your new home.

Moist Air Movement

Clothes dryer exhaust systems pose a different problem than other home exhaust systems because the air is moist.  The air from the dryer must exhaust to the exterior of the home to prevent damage from excessive moisture buildup.  A dryer vent that discharges into an attic or crawl space with wood members can lead to degradation of materials and possible mold problems.

Backdraft Damper

All modern dryer vents should have a backdraft damper that seals off the vent when not in use.  This damper can be as simple as a flap that opens in the direction of the air flow by the force of the air from the dryer when it is operating.  This damper helps keep cold air from rushing into the home from the exterior when the dryer is not in use.  The damper can also prevent rodents, rain, snow and pests from getting into the home.

Length of Pipe for Clothes Dryer Exhaust Vent

When designing the clothes dryer exhaust vent for a new home, it’s important to consider the pipe length run.  We want to be sure the dryer exhaust blower fan will be able to push sufficient air volume to carry away the moist air and lint.  The length of the vent run should be considered carefully by reviewing the make and model of the appliance.  Most manufacturer directions that come with the dryer will give detailed instructions as to the proper vent design for the particular model being installed.

In general, the maximum length of a clothes dryer exhaust vent should not be greater than 25 feet from the dryer’s location to the wall or roof termination to the exterior.  But we can’t just consider the overall pipe run length.  We also need to review the number and degree of any bends in the pipe as these add resistance to the flow of air.  So, the more bends that are in the pipe, the shorter the dryer exhaust vent run can be.  For each 45 degree bend in the vent, the overall length should be reduced by 2-1/2 feet.  For each 90 degree bend, the maximum length is reduced by five feet.

Hard versus Flex Pipe

So what type of material is ideal for clothes dryer exhaust vents?  Hard, smooth pipes are the best.  These are resistant to being crushed and provide less resistance to the air flowing through them.  If a flexible type of duct vent is used, be sure the run doesn’t become kinked in any way.  It’s also important to check the flexible ducts regularly as these are more prone to buildup of lint because of the increased resistance to air flow.


Regular maintenance will help keep your dryer working safely and efficiently.  The exhaust pipe should be checked regularly for lint buildup or other obstructions that might block the flow of air.  The exterior termination point should also be reviewed to make sure there’s nothing obstructing the opening.  Things like snow, ice, bird nests, lint…etc. can really cause problems.

One other vary important item to note:  If your dryer shuts down early without being turned off, it could be a sign that there is an obstruction in the exhaust vent pipe.  A clog in the vent can create a potential fire hazard, so be sure to review the venting prior to running the dryer again.

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