Clothes Dryer Ducting & Venting

According to FEMA, there are about 15,600 fires, 15 deaths, and 400 injuries every year that are caused by clothes dryer fires. Seventy per cent of the fires are attributed to "failure to clean". Failure to clean means more than just "remove the lint from the lint filter after each cycle". This blog will address the most common issues related to dryers and dryer duct materials and maintenance.

First, some basics. A full load of wet clothes contains as much as 1.5 gallons of water. No homeowner would consider pouring 1.5 gallons of water on the basement floor, inside of a crawlspace, or into an attic each time a load of clothes was dried. So, every dryer should be vented. Failure to do this can cause considerable damage to the wood structure in the enclosed area and can also promote the growth of mildew and mold. Just as with bathroom vents, always, always vent the air to the outside of the building. Outside means outdoors, not just out of the immediate living area.

Dryer venting should not exceed the equivalent length of 25'. Each 90° elbow effectively adds 5' to the equivalent length. So, a vent pipe with 2-90° elbows reduces the possible length of the straight piping to a maximum of 15'. Always keep the vent pipe system as short as possible.

The American Household Appliance Manufacturers Association recommends the use of UL listed rigid aluminum or steel duct or spiral-wound aluminum flex hose. Vinyl (usually white) flexible hose should never be used for clothes dryer venting systems.

Vinyl Flexible Hose is Not Acceptable for Venting Clothes Dryers

In fact, smooth rigid ducting is preferred as it is easier to clean the inside surface and the inside surface provides no interruptions that can restrict airflow and increase turbulence (as can even occur with spiral wound aluminum hose). The smooth surface of a rigid duct prevents lint from collecting inside the vent. However, sometimes it is very difficult to install rigid duct by convoluted space restrictions and spiral wound aluminum flex hose must be used.

When attaching sections of straight pipe and elbows, do not use sheet metal screws which will act as lint traps. Always tape the joints using UL-181 Approved metal foil tape. This is true for rigid steel and aluminum duct or aluminum spiral wound aluminum flex hose.

Typical Metal Foil Tape

Blockage of dryer venting systems is the most prevalent cause of clothes dryer fires. Blockage of the system reduces the airflow and can create a highly flammable fuel source. Failure to keep the system lint-free will also lengthen the drying time for each load. A clothes dryer must work much harder to move the moisture and lint through the ducting and can cause some dryer components to fail. Clean the lint filter after every load. Some clothes and materials (fuzzy blankets, coats, etc.) can completely block the lint filter after a single cycle.

A secondary source of blockage can occur at the outside wall damper. If there is no damper, birds and bees can enter and build homes that severely restrict the required air flow. The wall damper can also become clogged with large collections of lint. All clothes vent systems should exit through a wall damper that prevents infiltration by insects and bees. Homeowners should make a habit of checking the outside wall damper at least once a month. If you can't remember, put it on your calendar. My wall damper exits near the patio, so I try to make a visual check whenever I pass by.

Typical Louver Type Wall Damper
(dryer is operating in photo)

In summary:

• Clean out your lint filter after each dry cycle
  
• Keep the length of the vent pipe system as short as possible and always no longer than 25'
  
• Install an outside wall vent that will prevent bees and birds from entering
• Always duct the system to the outdoors
• Never use vinyl hose as your ducting material
  
• Attach sections of vent piping using UL-181 Approved metal foil tape--never use screws
• Inspect your duct system periodically to make certain that it is providing a clean, clear path to the outdoors
• Inspect your outside wall vent ever month to make certain that it is functioning properly
• Never place items such as plastic, foam, or other synthetic materials that can increase the risk of fire
• If you notice that clothes, such as jeans, towels, or blankets are taking a long time to dry or that the clothes feel hotter than usual at the end of the cycle, inspect your lint filter and vent system for blockages.