A grease-clogged filter is the most common reason a range hood runs but no longer pulls air effectively — not a failed motor. After the filter, a blocked or leaking duct run, a stuck damper, and a worn fan motor or belt are the next most likely causes, roughly in that order of how often each actually turns out to be the problem.
Clean the grease filter first
- Remove the metal mesh filter
Usually held in place by simple clips or slides on the underside of the hood.
- Soak in hot water with dish soap
About 20 minutes is generally enough to loosen accumulated grease and dust.
- Scrub and rinse thoroughly
A dishwasher on its hottest cycle also works well for a deeper clean if the filter is heavily soiled.
- Dry fully before reinstalling
A damp filter left back in place can drip and re-collect residue faster.
Most range hood airflow complaints resolve at this step alone — it is worth doing before assuming anything mechanical has failed.
Check the ductwork for blockages or leaks
With the filter clean but airflow still weak, check the duct itself. Grease buildup accumulates inside the ductwork over years, not just on the visible filter, and can restrict airflow the same way a clogged filter does. Use a flashlight to check what you can see of the interior, and check the exterior vent cap for debris, leaves, or nesting blocking the outlet. Separately, any leak in the duct run — a loose joint or a gap in the connection — reduces the pressure the fan can build, which shows up as weak airflow even with a perfectly clean filter and a healthy motor.
Check the damper
The damper is a small flap, usually positioned just above the fan, that is supposed to open when the hood runs and close when it is off to keep outside air from flowing back in. If it is stuck closed, or only partially opens, air cannot exit through the duct even though the fan is running normally. Check that it moves freely and is not obstructed by grease buildup of its own.
Motor and fan issues
| Symptom | Likely cause |
|---|---|
| Fan runs but airflow feels weak everywhere | Clogged filter or duct — check those first |
| Fan sounds strained or louder than usual | Dirt buildup on the motor, or a worn belt on belt-driven models |
| Fan runs unevenly or vibrates | Damaged or warped fan blades not moving air efficiently |
| Fan does not run at all | Electrical/switch issue — see below, rather than the fan itself |
Electrical and switch problems
If the fan does not respond at all rather than running weakly, the switch itself may not be sending enough power to the motor. Check the breaker feeding the circuit before assuming a fan or motor failure — a straightforward, low-cost thing to rule out first.
When to call a professional
Because a clogged filter accounts for the large majority of “not venting” complaints, always start there and reassess before moving further into the ductwork or motor. If airflow is still weak with a clean filter, no visible duct blockage, and a freely moving damper, a worn motor or belt is the most likely remaining cause and is worth having a technician inspect.
