TinnerFlowTinnerFlow™
Apprentice Q&A · #365

Why does a reversed backdraft damper stop exhaust airflow?

2nd YearYELLOW · Check FirstBackdraft Damper Reverse

Short answer

Backdraft dampers are directional. If the fan closes the blades instead of opening them, pull and reinstall the damper in the correct airflow direction.

Field answer

A backdraft damper is supposed to open with fan flow and close when the fan shuts off. If it is reversed in a louver sleeve, the fan can press the blades shut and make the system look blocked.

Check the airflow arrow, blade swing, and fan direction. Remove the damper frame, flip it to the correct direction, and test that the blades swing freely before reconnecting the duct or sealing the sleeve.

What to check first

Do not do this

Do not force exhaust through a damper that is being pushed closed by the fan.

Why it matters

A reversed damper can create zero airflow, fan noise, vibration, and failed commissioning.

Ask foreman

The backdraft damper at [location] appears reversed; the fan flow is closing the blades. I checked blade swing and airflow direction. Do you want me to pull and flip the damper frame?

Text this wording

Related Field Rescue route

Open routeBack to Q&A

Final direction belongs to the foreman, approved drawings/specs, manufacturer instructions, pressure/material schedule, employer policy, and AHJ/code requirements.