What you need to know about dryer vent safety to protect your family and home
3 Practical Dryer Vent Requirements Every Homeowner Should Know
A vent that exhausts moist air to the home’s 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.
2. Dryer Vent Safety: No Restrictions
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 elbows are available which is designed to turn 90° 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.
3. Dryer Vent Safety: Lint Accumulation
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.
National Fire Protection Association: Fires Started by Dryers Statistics
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 Association.
- In 2010-2014, U.S. fire departments responded to an estimated average of 15,970 home structure fires involving clothes dryers or washing machines each year.
- These fires caused annual averages of 13 civilian deaths, 444 civilian injuries, and $238 million in direct property damage.
- The vast majority of fires (92%) involved clothes dryers.
- The leading items first ignited in dryer fires were dust, fiber or lint (26% of total) and clothing (26%), while items first ignited in washing machine fires were part of the appliance itself, including wire or cable insulation (26%), appliance housing or casing (24%), and drive belt (11%).
Code Recommendations for Clothes Dryer Exhaust
M1502.5 Duct construction.
Exhaust ducts shall be constructed of minimum 0.016-inch-thick (0.4 mm) rigid metal ducts, having smooth interior surfaces, with joints running in the direction of air flow. Exhaust ducts shall not be connected with sheet-metal screws or fastening means which extend into the duct.
This means that the flexible, ribbed vents used in the past should no longer be used. They should be noted as a potential fire hazard if observed during an inspection.
M1502.6 Duct length.
The maximum developed length of a clothes dryer exhaust duct shall not exceed 35 feet from the dryer location to the wall or roof termination. The maximum length of the duct shall be reduced 2.5 feet for each 45-degree (0.8 rad) bend, and 5 feet for each 90-degree (1.6 rad) bend. The maximum length of the exhaust duct does not include the transition duct.
- The IRC will defer to the manufacturer’s instruction, so if the manufacturer’s recommendation permits a longer exhaust vent, that’s acceptable. An inspector probably won’t have the manufacturer’s recommendations, and even if they do, confirming compliance with them exceeds the scope of a General Home Inspection.
- The IRC will allow large radius bends to be installed to reduce restrictions at turns, but confirming compliance requires performing engineering calculation in accordance with the ASHRAE Fundamentals Handbook, which definitely lies beyond the scope of a General Home Inspection.
Exhaust ducts shall terminate on the outside of the building or shall be in accordance with the dryer manufacturer’s installation instructions. Exhaust ducts shall terminate not less than 3 feet in any direction from openings into buildings. Exhaust duct terminations shall be equipped with a backdraft damper. Screens shall not be installed at the duct termination.
Inspectors will see 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. Sometimes they will terminate just beneath attic ventilators. This is a defective installation. They must terminate at the exterior and away from a door or window. Also, screens may be present at the duct termination and can accumulate lint and should be noted as improper.
M1502.3 Duct size.
The diameter of the exhaust duct shall be as required by the clothes dryer’s listing and the manufacturer’s installation instructions.
Look for the exhaust duct size on the data plate.
M1502.4 Transition Ducts.
Transition ducts shall not be concealed within construction. Flexible transition ducts used to connect the dryer to the exhaust duct system shall be limited to single lengths not to exceed 8 feet, and shall be listed and labeled in accordance with UL 2158A.
M1502.4.2 Duct installation.
Exhaust ducts shall be supported at intervals not to exceed 12 feet and shall be secured in place. The insert end of the duct shall extend into the adjoining duct or fitting in the direction of airflow. Exhaust duct joints shall be sealed in accordance with Section M1601.4.1 and shall be mechanically fastened. Ducts shall not be joined with screws or similar fasteners that protrude more than 1/8-inch into the inside of the duct.
Additionally, makeup air for the laundry room in an amount equal to the sum – in cubic feet per minute (CFM) – of the dryer vent fan, and of any laundry room fans, must be supplied when both fans are operating. Depending on the laundry room’s size, this may approach 300 CFM. Makeup air would need to be supplied from some source. If the door is closed and there is no window, this may present a problem, including extended drying times and reduced dryer vent flow that can cause an excess accumulation of lint in the exhaust vent, which is a potential fire hazard.
Schedule your Annual Home Maintenance Inspection.
Even the most vigilant homeowner can, from time to time, miss small problems or forget about performing some routine home repairs and seasonal maintenance. That’s why an Annual Home Maintenance Inspection will keep you aware of your home’s condition and help you prevent it from suffering serious, long-term, and expensive damage from minor issues that should be addressed now.
Just as you regularly maintain your vehicle, consider getting an Annual Home Maintenance Inspection as part of the cost of upkeep for your most valuable investment…your home.
Your future deserves the attention of a professional. If you have questions or would like more information on a Home Maintenance Inspection, please contact Micah Stephens with SafeShield Inspections, LLC at (832) 953-6992 or email Micah@SafeShieldInspections.com. CLICK HERE for a free quote.