M1502.6 Duct length. The maximum length of a clothes dryer exhaust duct shall not exceed 25 feet (7,620 mm) from the dryer location to the wall or roof termination. The maximum length of the duct shall be reduced 2.5 feet (762 mm) for each 45-degree (0.8 rad) bend, and 5 feet (1,524 mm) for each 90-degree (1.6 rad) bend. The maximum length of the exhaust duct does not include the transition duct.

This means that vents should also be as straight as possible and cannot be longer than 25 feet. Any 90-degree turns in the vent reduce this 25-foot number by 5 feet, since these turns restrict airflow.
A couple of exceptions exist:

  1. The IRC will defer to the manufacturer's instruction, so if the manufacturer's recommendation permits a longer exhaust vent, that's acceptable. An inspector probably won't have the manufacturer's recommendations, and even if they do, confirming compliance with them exceeds the scope of a General Home Inspection.
  2. The IRC will allow large radius bends to be installed to reduce restrictions at turns, but confirming compliance requires performing engineering calculation in accordance with the ASHRAE Fundamentals Handbook, which definitely lies beyond the scope of a General Home Inspection!
 
Posted by Eragorn Northe on 02/11/2010 01:27 PM   Comments (4)  
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4 Comments on Dryer Vent Safety

FEB
11
2010
184,341 Points 2 Featured Posts

Thanks for the info... Never knew that the bends made a difference.  Oh, the Lions and the Riders meet up again in a few months.. Good times...
4:44pm • #1
FEB
16
2010

I find some pretty interesting dryer runs in older homes here, such as this beauty:

Interesting dryer duct
10:04am • #2

Thats some picture Russel,

Darren are you a Riders fan or a Lions fan?
10:44am • #3
FEB
18
2010
165,839 Points 8 Featured Posts Outside Blog Called Shot Master

Thanks for the information!  Very helpful...I am going to reblog this.
5:55am • #4


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Eragorn Northe

Moose Jaw, SK

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