Proper Venting for Dryers

As a home inspector, one of the most common problems I encounter in homes is improper dryer venting.  Seems simple, what can go wrong?  Well, a few simple things done wrong can have the potential to burn your house down, cause thousands of dollars of mold damage, or just waste energy and take longer to dry your clothes.

Length: The shortest run is the best run.  25' max is the gold standard.  There is a reduction in length of 5' for each 90 degree turn, ie. if you have 2 90 degree turns, then your maximum length should be 15'.

Materials: Dryer vent should NOT be plastic.  This has the potential to melt and catch fire.  This includes the foil looking mylar type vents.  Vent pipe should be metal pipe or flexible metal dryer vent material, which is a heavy aluminum tube that can be bent.  White PVC pipe should never be used as it can build a static charge that can ignite lint buildup.

Correct vent materials

Incorrect plastic vent also showing how lint can block air flow.

Securing sections: Screws should not protrude into the air pathway.  Use foil tape (not duct tape) and clamps to connect sections.

So, the fire hazard should be obvious, but what about the other things I mentioned.  Dryer vents not ducted to the exterior can be a major contributor to mold/mildew in attic or other spaces.  I've inspected houses where major mold remediation was needed based on the dryer vent ducting into an attic or more commonly a crawlspace.  Think about how much water is in those heavy clothes when you put them into the dryer.  If not ducted to the exterior, this goes right into your enclosed space, and moisture is one of the building blocks for mold growth.

Cleaning: It is recommended that dryer vents be cleaned annually or semi-annually.  Sometimes, if it's in your basement and accessible, it's easiest to just replace the metal vent pipe.  In some houses, there are long fixed runs of metal vent duct that need cleaning with a vacuum/brush etc.  Some homeowners choose to do this themselves, others contract duct cleaning companies.  Hint; when a professional company is on site, have them clean your bath exhaust vents as well (they can also make sure your bath vents are ducted to the exterior as well).

This amount of blockage is very common.

Lastly, be sure you're not using a ventless type lint collector.  Although the home centers sell them, they put large amounts of moisture into your house.  I can't tell you how many moldy basements I've been in due to a ventless lint collector being installed.  The homeowner saved a few pennies on their heating bill but paid thousands in mold remediation not to mention creating and living in an unhealthy environment for years. 

Ventless lint collector installed with incorrect vent duct.

Hope this basic info helps you.  Correct materials, correct lengths and regular cleaning can make your house safer and the faster drying times will save energy.