A clear dryer duct can save energy and prevent a fire

By Arnie Katz
A clear dryer duct can save energy and prevent a fire

Don’t let a blocked dryer duct cause a fire.

Q: The termite guys were in my crawlspace doing an inspection, and they told me the dryer duct was partially crushed. They said this is dangerous and can cause a fire, and that the type of ducting I have is a flexible plastic that is no longer even allowed for venting dryers, and that I should replace it immediately. It's worked fine for 30 years, although I have noticed the clothes take much longer to dry lately. Do I really need to worry about this, or are they just blowing smoke?

A: You need to do something about it. And you might want to put your termite guys on your Christmas list. They may have saved your home. Thousands of house fires are started every year in dryers, and one of the main causes is lint buildup and other blockages in the vents.

The dryer works by blowing air over a heater (either gas or electric) through the clothes and then out of the vent and through the duct to the outside. The air blowing through the clothes picks up particles of the fabric (lint) that are carried out with the hot air.

Most of the lint is captured by the filter, but in many dryers, because the filter doesn't fit really tightly, some of the lint gets past the filter and into the duct. If there are any obstructions in the duct, the lint is more likely to collect on the sides, build up and slow down the air flow.

If the air is moving more slowly, it will take longer to dry your clothes, and that will require more energy. If the air flow is blocked enough, it can cause the dryer to overheat, which can cause the dryer to fail long before its expected life.

In some cases, this overheating causes fires.

The first thing to do is to find the exhaust termination of your dryer duct. This usually is through the foundation wall, if you have a basement or crawlspace. In a two-story home, it may come through the space between the first floor ceiling and the second floor; or it may come out through the attic.

In your case, you know it's coming through the crawl space. If you can't find it, go look in the crawl space. Sometimes dryers are just dumping the moisture and lint into the crawl space, which is an excellent way to grow serious amounts of mold. If the dryer isn't vented clear through to the outside, you need to get that done.

Once you know where it ends, turn on the dryer and make sure a lot of air is coming out of the duct at its termination. If it's not, you know you have a serious restriction. Take off the cap and see if you can see lint buildup along the sides of the duct. If there is buildup, you need to clean it. You may have to take the duct apart to do that.

If you have the plastic or foil type ducts, this would be a good time to replace as much of it as possible with smooth metal duct work. You can easily find this at home improvement stores, usually in 3-foot sections. If there are areas where you need to use the flexible ducting, use the metal type and pull it so that it is as straight as possible.

Use as few bends and turns as you can, and put the duct sections together with tape. Don't use screws, as they stick into the duct and collect lint. And make the duct as short as possible. The manual for your dryer will tell you the maximum length it can safely be.

In addition to cleaning the filter before or after every load, everyone should check their dryer vents a couple of times a year and clean them if necessary. This will get your clothes dried quicker and save you few bucks on your energy bills. And it may just prevent a fire.

About the Author

Arnie Katz is the former building science consultant for Advanced Energy in Raleigh. advancedenergy.org

Comments (3)

  • alena


    30 May 2014 at 15:30

    You hear of fires all the time starting because of blocked ducts. That is one thing I am careful to checked. I always make sure that I check the ducts monthly.



  • John


    27 June 2014 at 13:51

    That is definitely something that I don't want happening to me. It would be pretty rough to come home and find out that the clothes you put in your dryer was what caused the fire. I think I'm going to check my dryer duct and replace it if I need to.


  • Wally West

    Wally West

    13 February 2015 at 10:45

    My wife noticed that our dryer duct was not venting properly and it has me concerned. I have heard of fires like these and it makes me want to call a repairman immediately. I am glad that my wife said something because I would probably never know. I will call someone and have them come out to the house and replace the duct for us.


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