I recently Inspected a home in Richmond, VA. Occasionally, I will see a plastic dryer vent in the house and I write it up as a defect and explain to the buyers the safety hazard. A few times I have seen a flexible metal vent going through the crawl space which is also not a recommended practice. This home was a first for me but I was not surprised. The dryer vented through a plastic duct all the way through the crawlspace. This is a very bad idea and if you read the rest of this article you will know why.
InterNACHI believes that house fires caused by dryers are far more common than are generally believed, a fact that can be appreciated upon reviewing statistics from the National Fire Protection Agency. Fires caused by dryers in 2005 were responsible for approximately 13,775 house fires, 418 injuries, 15 deaths, and $196 million in property damage. Most of these incidents occur in residences and are the result of improper lint cleanup and maintenance. Fortunately, these fires are very easy to prevent.
Clothes dryers evaporate the water from wet clothing by blowing hot air past them while they tumble inside a spinning drum. Heat is provided by an electrical heating element or gas burner. Some heavy garment loads can contain more than a gallon of water which, during the drying process, will become airborne water vapor and leave the dryer and home through an exhaust duct (more commonly known as a dryer vent).
A vent that exhausts moist air to the home exterior has a number of requirements:
It should be connected. The connection is usually behind the dryer but may be beneath it. Look carefully to make sure it’s actually connected!
It should not be restricted. Dryer vents are often made from flexible plastic or metal duct, which may be easily kinked or crushed where they exit the dryer and enter the wall or floor. This is often a problem since dryers tend to be tucked away into small areas with little room to work. Vent hardware is available which is designed to turn 90 Deg in a limited space without restricting the flow of exhaust air. Restrictions should be noted in the inspector’s report. Airflow restrictions are a potential fire hazard!
One of the reasons that restrictions are a potential fire hazard is that, along with water vapor evaporated out of wet clothes, the exhaust stream carries lint, highly flammable particles of clothing made of cotton and polyester. Lint can accumulate in an exhaust duct, reducing the dryer’s ability to expel heated water vapor, which then accumulates as heat energy within the machine. As the dryer overheats, mechanical failures can trigger sparks, which can cause lint trapped in the dryer vent to burst into flames. This condition can cause the whole house to burst into flames! Fires generally originate within the dryer but spread by escaping through the ventilation duct, incinerating trapped lint, and following its path into the building wall.
Transition ducting from the dryer should be metal not plastic. Plastic ducting melts and promotes the spread of a fire. Although metal ducting is not fire proof is will allow time to identify and extinguish a fire.
Keep your dryer vents clean. Boy scouts are taught to bring lint with them on camping trips. This is because lint is very flammable and helps to start camp fires. A dirty dryer vent is very flammable. You should have your dryer vents cleaned at least once every six months