Over 24,000 house fires and nearly $100 million in property damage occur each year due to improper dryer vent installations and other problems. The fires and damage can be avoided by inspecting your dryer vent line occasionally. If your dryer has been in service for 4 or 5 years without an inspection, or especially if you have noticed that it seems to be taking a lot longer to get the clothes dry; you need to inspect the vent line (or hire someone to inspect it for you).
Clothes dryers have a built in screen to catch lint. These should be cleaned on a regular basis- preferably every time you run a new load of clothes through the dryer. Most people are pretty good about doing this. However, these screens don’t catch all of the lint produced by the dryer and lint can begin to accumulate in the dryer vent line or at the exterior cap where the dryer vent terminates. If this happens it can cause big problems! For one thing, if the vent line becomes completely clogged, the heated air from the dryer won’t be able to flow like it’s supposed to. This means that you will have to run your dryer much longer to get the clothes dry, which of course costs more money. Even worse, it may allow your dryer to overheat because the heat that the dryer is producing can’t be carried away if the vent line is clogged. The picture below shows a clogged dryer vent line in an attic at a friend’s house. They had noticed that the dryer was taking longer to get the clothes dry. The green vent line is pvc, which is an improper material (more on improper materials later). I discovered this when I inspected their house. They were in the process of taking out the pvc and installing a new metal vent line when they saw that the old line was clogged with lint. This is the type of situation that needs to be fixed.
2 TYPES OF DRYER VENT LINES:
There are actually 2 types of dryer vents (depending on their location), and the requirements for each vary slightly: 1. The appliance vent line (aka transition duct): This vent line goes from the dryer to the wall. Obviously, this is the dryer vent that you can easily see if you look behind your dryer. The appliance vent line should be no more than 8 feet in length. The vent should not be concealed and shouldn’t be damaged or crushed. Also, it should be listed and labeled in accordance with UL (Underwriters Laboratory) 2158A. The white vinyl appliance line (pictured below) is not approved- Vinyl can melt and catch on fire if overheated. Mylar foil (looks like aluminum foil) vents are available and are ok to use if they are UL listed. Also, there are semi-rigid aluminum vents. Some of these are approved and some aren’t- Look for the UL listing. The best dryer appliance vents that I have seen (pictured below) were found at home improvement stores Home Depot and Lowes in the appliance accessories section. One was $25 and the other one was $30. Note that both have a UL listing (circled). You can read more about the one pictured at right at Reuben Saltzman’s expert blog at: http://structuretech1.com/dryerflex-a-superior-dryer-transition-duct/
2. The house vent line: This vent line is the one that is typically behind the wall. It usually goes to an exterior wall or up through the attic and through the roof. Generally, these vent lines should vent to the exterior although there are some UL listed devices that will allow you to vent to the interior of the house. This is not recommended however. Drying a full load of clothes can remove as much as a gallon of water from the clothes. If your dryer vent is venting to the interior of your home, all that water vapor will be dumped into the house or garage. Especially in the humid summer months, this is not desirable. The length of the house vent line should not be excessively long. Manufacturers publish the maximum length allowed. Other details: The duct should be 4 inches in diameter (no more/ no less), smooth metal (no vinyl, pvc, or mylar foil). There must be no sheet metal screws protruding into the vent which could catch lint. (The best way to connect joints is with foil tape, not sheet metal screws). At the point at the exterior where the vent line terminates, a cover is required. The cover should have a damper (aka flapper) so it will close when the dryer is not running to prevent air, insect, and vermin entry into the house. And finally, there should not be a screen present because this can collect lint over time and you can end up with the clogged vent problems as described before.
If you're setting up a new dryer or if you’ve been using a dryer for many years without inspecting for lint build up, following these precautions will help make sure everything is working safely. --- Kim Christensen ACI, TREC 20358