From 2006-2010, the National Fire Protection Association (NFPA) estimates that U.S. fire departments responded to an estimated average of roughly 14,000 home structure fires involving dryers per year, resulting in an average of roughly 30 civilian deaths, 400 civilian injuries and $191 million in direct property damage annually. The dryer vent is the mechanical exhaust system for the clothes dryer. The heat provided by an electrical heating element or gas burner allows the clothes dryer to evaporate the water from wet clothing as the clothes tumble inside a spinning drum. A clothes dryer will vent about a gallon of water for each load of laundry. During the drying process the water becomes airborne water vapor, and leaves the dryer and home through an exhaust duct also known as a dryer vent. A dryer vent should always exhaust to the exterior of the home. During our inspections we have seen many dryer vents terminate in crawlspaces or attics where they deposit moisture, which can encourage the growth of mold, wood decay or other material problems, but we will get to proper termination in another blog.
COMPONENTS OF A DRYER VENT
Dryer vents typically have a transition duct and an exhaust duct. The transition duct is the visible, flexible section of duct connecting the clothes dryer to the exhaust duct. The exhaust duct runs through or beyond floors and walls of the house to exhaust the air from the dryer to the exterior.
The following is a picture of a flexible duct connected to the dryer, this is acceptable:
However, this flexible duct should always be visible. It must not be concealed within construction. Therefore it should never be used through or beyond floors and walls according the International Residential Code (IRC). IRC - M1502.4.3 Transition Duct.
Transition ducts used to connect the dryer to the exhaust duct system shall be a single length that is listed and labeled in accordance with UL 2158A . Transition ducts shall be not greater than 8 feet (2438 mm) in length. Transition ducts shall not be concealed within construction.
The following are defects found during our home inspections. You can see in the photos that the flexible ducts are running through the walls/floors which is not permitted according the IRC.
Flexible duct running through or beyond floors and walls has been found to be a potential fire hazard. Flexible ducts trap lint between creases which can clog the duct, requiring the dryer to work harder and longer to dry clothes. This increases the dryer's temperature. The combination or an increase in heat and accumulated flammable lint in the duct leads to a potential fire hazard. To prevent a fire hazard, the flex duct should transition to a rigid metal duct before penetrating through the wall. The following photo shows the flex duct transitioning to a rigid metal duct before penetrating the wall, this is acceptable, as rigid metal ducts have a smooth interior finish.
WHAT MATERIAL SHOULD BE USED THROUGH OR BEYOND FLOORS AND WALLS?
International Residential Code - M1502.4.1 Material and Size Exhaust ducts shall have a smooth interior finish and shall be constructed of metal not less than 0.0157 inch (0.3950 mm) in thickness (No. 28 gage). The duct shall be 4 inches (102 mm) nominal in diameter.
The following photo on the left shows a flexible duct being run beyond floors and walls. The photo on the right shows a rigid metal duct with a smooth interior, being used beyond floors and walls. As you can see, the hard, smooth duct is the safe and acceptable material for running through and beyond floors and walls.
If you have flexible duct running through your walls or floors, the creases can allow lint to build up. This is a potential fire hazard! We recommend having the duct work evaluated and replaced by a qualified HVAC professional for you and your family's safety!
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