Kitchen Hoods and Grease Exhaust Systems

What does a kitchen exhaust system do?

Kitchen grease exhaust systems are installed to remove excess heat, odor, smoke, and grease-laden air from the immediate cooking area. A properly-designed system should have enough structural integrity and clearance from flammable materials to be able to contain a small grease fire inside it until the grease burns up, but if there is too much grease built up, no system will contain it.

Why Clean It?

Fire Prevention

  • The main reason is to prevent a fire from starting within the ductwork or spreading through the ductwork from cooking equipment under the hoods.
  • The less grease build-up, the less fuel there is to burn.

Insurance Coverage

  • Many insurance companies refuse to provide coverage for restaurants unless they have an up to date maintenance contract covering a thorough cleaning on a regular basis.
  • The required frequency of service varies by the volume of the restaurant.

Cost Reduction

  • The fan assembly is the “heart” of the exhaust system.
  • It must be cleaned to reduce the number of service calls to replace burned out motors, unbalanced fan wheels, and worn out shafts and bearings.

How Often? NFPA Standards

Obviously, as often as sufficient grease accumulates within the system to constitute a fire hazard, but the frequency depends on the following:

  • The type and volume of cooking one does each day
  • The equipment used, such as grease filters, grease extractors, and “water-wash” hoods to prevent grease from entering and accumulating within the system.
  • General maintenance of the system. In order for grease catching and removing devices to function properly, hoods must be cleaned regularly.
  • The National Fire Protection Association's NFPA 96 Standard specifies frequencies for inspection, not cleaning.  Those standards are shown below.

NFPA 96 - 12.4 Exhaust System Inspection Schedule

Type or Volume of Cooking Frequency
Systems serving solid fuel cooking operations Monthly
Systems serving high-volume cooking operations such as 24-hour cooking, charbroiling, or wok cooking Quarterly
Systems serving moderate-volume cooking operations Semiannually
Systems serving low-volume cooking operations, such as churches, day camps, seasonal businesses, or senior centers. Annually


How do I check my system?

  • Remove the filters or grease extractors and shine a flashlight into the interior chamber and ductwork.
  • Remove the access/inspection panels in the horizontal run of ductwork and check the interior for liquid or encrusted grease.
  • Turn off the exhaust fan and check the blades of the fan wheel to see if they are free of grease/dirt build-up. Just a coating of grease causes the fan to work harder and become unbalanced.

What should I consider to be clean?

According to NFPA-96 section 11.6.2: “Hoods, grease removal devices, fans, ducts, and other appurtenances shall be cleaned to remove combustible contaminants prior to surfaces becoming heavily contaminated with grease or oily sludge.”

What risks am I exposed to in not properly cleaning a kitchen exhaust system?

Grease and particulate buildup in the exhaust system is a fire hazard, and greatly impacts on the efficiency and lifetime of mechanical equipment. According to the National Fire Protection Association, the majority of restaurant fires originate on the kitchen cooking appliances and flare into the kitchen exhaust system. If the entire exhaust system is not cleaned, a significant risk for fire exists whenever cooking appliances are used.