CSLB C-20 HVAC ContractorVentilation and Air DistributionMedium
Per the California Mechanical Code and referenced NFPA 96 provisions, what is the minimum required clearance from an unenclosed, unlisted commercial kitchen grease exhaust duct to combustible construction?
- A18 inches
- B6 inches
- C36 inches
- D9 inches
Show answer & explanationAnswer & explanation
Correct answer: A. 18 inches
Standard unlisted grease ducts must maintain a minimum 18-inch clearance to combustible materials unless the duct is enclosed in a fire-rated shaft or uses a listed factory-built grease duct enclosure system with reduced clearance requirements.
Why the other options are wrong
- B. 6 inches is inadequate for grease duct fire safety.
- C. 36 inches exceeds the standard requirement and is not the baseline figure.
- D. 9 inches is still below the required standard clearance.
Grease Duct Clearance
Commercial kitchen grease exhaust ducts require a minimum 18-inch clearance to combustible construction unless enclosed in a rated shaft or a listed reduced-clearance enclosure system per NFPA 96 and the CMC.
- Standard clearance is 18 inches for unenclosed ducts
- Listed enclosure systems can reduce required clearance
- Grease ducts pose fire risk from accumulated grease residue
Memory trick: Eighteen inches keeps the grease fire from the frame.