Hood Not Pulling Air / Weak Suction

What's causing it

The most common cause is grease-saturated baffle filters that have gone too long without cleaning, which physically block airflow through the hood. Beyond the filters, grease accumulation inside the duct itself narrows the passage and chokes suction at the source. A failed or underperforming exhaust fan motor is another frequent culprit, especially in high-volume kitchens where the fan runs continuously. Belt-driven fans can lose tension over time, reducing RPM without triggering an obvious alarm. In some cases, a blocked or improperly balanced makeup air system creates negative pressure that counteracts the hood's draw.

What happens if you wait

A hood pulling weak suction means smoke, grease vapor, and combustion byproducts are staying on the line instead of being exhausted out of the building, creating poor air quality for your crew and a fire risk from grease accumulation in the duct. Health inspectors treat ventilation failures as active violations, and a cited hood system can trigger a re-inspection timeline or conditional permit status. Grease-laden ducts that continue operating without adequate airflow are a leading cause of commercial kitchen fires, which puts your property, your staff, and your license at risk.

LA County Environmental Health and the LAFD both require functional exhaust ventilation as a condition of operation, and a hood system failing to clear smoke and grease vapor is citable under both health code and NFPA 96 standards for commercial cooking ventilation.