Exhaust Systems

An exhaust system consists of a hood or canopy, a fan and duct system, and grease-removal equipment.


Hoods should be made of stainless or carbon steel or other approved fire-resistant material. They should extend completely over all equipment that produces grease-laden vapors.

Properly designed hood


A duct system is a passageway that transmits grease-laden vapors to the outside. Ducts should consist of fire-resistant materials, be isolated from other exhaust or ventilation systems, and lead directly to the exterior. Qualified personnel should also maintain and clean ducts regularly.

A typical fan duct system


Fans move air and grease-laden vapors to the duct system. Fans and motors should be UL listed for use in grease-laden atmospheres and have blades of nonferrous metal, such as aluminum.

Fire wrap is an acceptable duct insulation

Grease filters and extractors

Those systems help rid hoods of grease. Commercial cooking operations require metal filters. They should be UL-listed.

Hazardous accumulation of grease in the exhaust system
Hazardous accumulation of grease in the hood and duct


Exhaust systems should meet the following clearance criteria:

  • minimum of 18 inches from hoods and ducts to combustible material
  • minimum of 6 inches to noncombustible material if duct is enclosed
  • minimum of 10 inches from outlet to adjacent buildings
  • minimum of 10 inches from outlet to air intakes, space permitting