The technical guidance on this page reflects these published codes and standards, which your local authority (AHJ) adopts, amends, and enforces. It is educational, not engineering or legal advice — confirm the current requirements for your jurisdiction.
NFPA 96 sets exhaust cleaning frequency by cooking volume: solid-fuel monthly, high-volume quarterly, moderate-volume semiannually, and low-volume annually. The hood, filters, duct, and fan must be cleaned to bare metal by qualified personnel, and access panels must let cleaners reach the entire grease-bearing system.
Every time you cook, grease-laden vapor rises into the hood, passes through the baffle filters, and travels up the exhaust duct to the fan and roof. Some of that grease condenses and clings to metal along the way. Left in place it becomes a concentrated fuel load lining the exact path a flame would follow out of the kitchen, which is why grease-duct fires spread so fast. NFPA 96 treats scheduled cleaning as a fire-prevention requirement, not housekeeping, and fire inspectors, insurers, and health departments all enforce it.
Cleaning is not the same as the daily wipe-down of filters. Code-driven cleaning means the entire grease-bearing system, including the hood interior, filters, the full length of duct, and the exhaust fan housing, is degreased so that grease deposits are removed down to bare metal. Surfaces that cannot be brought to bare metal are noted, and inspection reports document the condition before and after.
NFPA 96 sets the minimum inspection-and-cleaning interval according to how much grease-laden vapor the operation produces. The current schedule (Table 11.4 in recent editions) breaks operations into four tiers:
| Frequency | Type of cooking operation | Typical examples |
|---|---|---|
| Monthly | Solid-fuel cooking | Wood-fired ovens, charcoal or mesquite grills |
| Quarterly | High-volume operations | 24-hour kitchens, charbroiling, wok cooking |
| Semiannually | Moderate-volume operations | Most sit-down restaurants and hotel kitchens |
| Annually | Low-volume operations | Churches, day camps, seasonal or occasional cooking |
These are minimums. A busy griddle-and-fryer line can build enough grease to warrant more frequent service than the table implies, and inspectors can require it. Note that some jurisdictions have adopted newer NFPA 96 language extending monthly cleaning to any operation running very long daily hours regardless of fuel; confirm the edition your authority having jurisdiction (AHJ) enforces.
NFPA 96 pairs cleaning with periodic inspection. The system must be inspected for grease accumulation at intervals based on the same cooking-volume categories, and cleaned whenever a measurable deposit is found. In practice a certified inspector checks the hood, filters, and accessible duct, measures or documents grease buildup, and either cleans on the spot or schedules service. If deposits are found, the surfaces must be cleaned to bare metal, not merely thinned out.
The takeaway for operators: the frequency table is the floor, but found grease drives the requirement. A kitchen technically on an annual schedule that is discovered with heavy buildup will be cited and required to clean immediately, and its interval will likely be shortened.
You can only clean what you can reach. NFPA 96 requires access panels or openings along the exhaust duct so the entire run can be inspected and cleaned, including horizontal runs and changes in direction where grease collects. Ducts must be built to allow this access, and panels must seal grease-tight when closed. If a cleaning crew cannot get to a section of duct, that section is a hidden hazard and a code deficiency.
After service, areas that are physically inaccessible must be noted in the cleaning report so the owner and AHJ know they were not reached. When a report repeatedly flags the same inaccessible sections, that is a signal the ductwork needs additional access panels retrofitted.
NFPA 96 requires that cleaning be performed by properly trained, qualified, and certified persons who are acceptable to the AHJ. In most areas that means a commercial hood-cleaning company whose technicians hold recognized certification. Kitchen staff can and should maintain the filters daily, but the full duct-to-fan cleaning is specialized work involving degreasers, containment, and often roof access.
A reputable cleaner will leave a dated certificate or sticker on the hood recording the cleaning date, the areas serviced, and any deficiencies such as inaccessible ductwork. Keep these records; they are what an inspector or insurer asks for, and a lapse in documentation is itself a violation. Cleaning also pairs directly with your fire-suppression service and overall ventilation, so many operators schedule hood cleaning and semiannual suppression inspection together.