What is the purpose of a backdraft damper in the exterior vent hood?

• A. To prevent outside air and pests from entering when the dryer is off
• B. To allow birds to enter for nesting
• C. To increase airflow into the house
• D. To humidify the vent

Answer: (B)

Backdraft dampers in exterior vent hoods act as a one-way gate for airflow. When the dryer pushes hot, moist air out, the damper opens to let that exhaust escape. When the dryer isn’t running, or if there’s a tendency for air to flow backward, the damper closes to block outside air from sneaking back into the ducts and into the living space. This helps prevent cold drafts, moisture intrusion, and entry of pests or birds, and it reduces energy loss from conditioned air escaping through the vent.

In other words, the device is there to stop backflow and keep the outdoors from coming indoors, rather than to push air into the house, humidify the vent, or encourage birds to nest.