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Clothes Dryer Vent Can Keep Out the Cold

July 24, 1994|Special to The Times

QUESTION: I read about some device I can attach to the outside of my house where my clothes dryer would exhaust--which will keep cold air from coming back inside when the dryer is not operating. Does this work? Will lint build up and plug the vent?

ANSWER: A back-draft damper is a device designed to help keep cold air, birds and rodents out of your dryer's exhaust duct. The duct opening should never be covered with a screen because the screen would get clogged with lint. The Uniform Mechanical Code requires clothes dryer exhaust ducts terminate outside the building and have back-draft dampers. Check with your local code official to learn of specific requirements in your area. The ability of back-draft dampers to prevent cold air infiltration varies with design and maintenance.

Most back-draft dampers have a flapper that hangs on a hinge over the exhaust vent opening when the dryer is off. The flapper covers the opening. When the dryer is on, the exhaust airflow forces the flapper to hinge open. Usually flapper dampers don't close completely airtight. They may not close as designed if damaged. Lint can collect on the flapper hinges and prevent proper closing. You should periodically clean the hinges and adjust the damper so it closes properly.

There is a dryer vent hood product designed to seal very tightly when the dryer is not on. The one we are aware of is made by Heartland Products in North Dakota. It's made of ABS plastic that can be painted. It can endure outside temperature extremes. Before dropping by your local hardware store, it's worth a phone call to make see if they carry the product.

In this design, the very end of the exhaust duct turns upward. An inverted cup sits upon the end of the duct, keeping it closed to bugs, rodents and air. When the dryer turns on, the exhaust airflow pushes the cup up, allowing the mixture of hot moist air and lint to escape. A guide keeps the cup aligned so it drops back down onto the opening when the dryer turns off. This whole assembly is enclosed under a hood. The hood keeps the rain out and protects the cup. You can easily remove the hood's cover to clean out the lint. You should check for lint buildup periodically throughout the year.

This design is more effective at sealing, and appears to be more durable. It eliminates the possibility of a sticky hinge caused by lint buildup. It may cost about $15 to $20 more than a typical flapper damper.

It's also important to install a dryer's exhaust ductwork correctly. The dryer's exhaust fan may not be strong enough to expel the lint if the ductwork is too long or too narrow. Lint buildup in the ductwork can reduce drying efficiency and create a fire hazard. The Uniform Mechanical Code limits the duct length, location and configuration for both metal and vinyl ducts.

Written by Mike Nuesa from the Education and Information Network of the Washington State Energy Office.

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