Installing Dryer Vents to Code

Direct heat and moisture outside with these guidelines.

The laundry room is one of three areas in a home, along with the kitchen and bathrooms, where a mechanical contractor installs exhaust vents. In the laundry area, an exhaust duct running to the exterior is installed to remove heat and moisture from the clothes dryer. If the dryer is fueled with propane or natural gas, the exhaust vent also removes combustion gases.

Removing moisture from the home is one critical function of exhaust vents. Moisture must be exhausted from the laundry area to protect interior finishes, drywall, lumber and other sensitive building materials. Removing heat from the dryer is also very important, as the dryer can start lint fires.

Here are a few guidelines for ensuring that a dryer vent is installed to code requirements:

  • Codes typically require that the dryer duct be no more than 25 feet long. It should be 2.5 feet shorter than 25 feet for every 45-degree bend and 5 feet shorter for every 90-degree bend. If the duct is more than 25 feet in length, the system requires a booster fan or a high-output dryer.
  • Ducts should be smooth metal with a minimum diameter of 4 inches. Flexible ducts should not be used, since they collect more lint and can easily be crushed, impeding airflow and potentially starting lint fires. The ducts should not have screws or connectors, which can collect lint, blocking the flow of combustion gases. Backdrafting can occur if the ducts are blocked, sending harmful carbon monoxide back into the home.
  • The male ends of the duct should face the direction of the airflow. The duct exhaust must not mix with or pass through other systems, such as the return-air plenum, because heat, moisture and combustion gases could mix with the conditioned air in the home.
  • The dryer exhaust duct should vent to the outside, and the vent should be at least three feet from any other opening. The vent should also have a termination cap and damper to keep vermin out of the home. There should not be a screen over the opening, since it could trap lint and cause a fire.

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