Exhaust duct specs for “Kitchen Exhaust Duct”

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Air duct specifications for “Kitchen Exhaust Duct” in air conditioning and ventilation systems.

Kitchen air duct systems are considered "special" systems because they must withstand high temperatures, grease, and high fan suction power. Much better than general air ducts Therefore, materials and specifications must be selected appropriately according to standards, , and


🧱 1. Types of air ducts in kitchen work.

Generally, kitchen work will have 2 main system.

System, function, design characteristics
Kitchen Exhaust Duct sucks in exhaust air, odors, grease. Must be resistant to heat and oil.
Make-up Air Duct fills in air (補fresh air) used to reduce negative pressure in the kitchen.

🧰 2. Pipe material used

Type Description
Black Steel Sheet is the most commonly used, thickness 1.2–1.6 mm (16–18 GA), coated with rust inside/outside.
Stainless steel (Stainless Steel 304) is used in kitchens, restaurants or hotels that require high cleanliness.
Galvanized pipe (GI) is not recommended because fat + high heat causes the zinc to deteriorate quickly.

⚙️ 3. Main standards and requirements

Item Specifications/Instructions
Pipe thickness 1.2 – 1.6 mm (16–18 GA) for main pipe, 1.0 mm for branch pipe.
Joints are fully welded to prevent oil leaks.
Insulation: Use 25 mm insulation (Fiberglass or Rockwool) + Aluminum Cladding if near walls or ceilings.
Access Doors must be at a distance not exceeding 3 meters for internal cleaning.
Slope has slope 1:100 To allow the oil to flow to the grease trap (Grease Trap).
Grease Trap / Drain Point: There must be a grease drain pipe under the air pipe line.
Fire Damper must not be installed inside kitchen pipes. Because it may become clogged from fat, use Fire-rated Duct instead.
Negative Pressure approximately –2.5 to –3.5 mmAq for Hood System

💨 4. Ventilation characteristics
 • Air speed in pipe : 1,200 – 1,800 fpm
 • Velocity at Hood : 1,500 – 2,000 fpm
 • The end of the Exhaust pipe must go outside the building > 3 meters from the opening.
 • Should have Backward-curved Exhaust Fan or Tube Axial with Grease Filter / Baffle Filter.

🏢 5. Example of choosing specifications.

Recommended spec list
Material: thick black steel 1.2 mm, fully welded.
Rockwool insulation 25 mm + Aluminum Sheet
Tube Axial Fan / Centrifugal Fan
Air speed in the pipe 1,500 fpm
Additional systems Drain Point, Access Door, Grease Cup

✅ Summary of things to remember
 • Kitchen pipes must be “fully welded” to prevent grease leaks.
 • Do not use galvanized (GI) pipe.
 • There must be an entrance for cleaning (Access Door).
 • Pipes and fans should be of fireproof material ≥ 1 hours.
 • The end of the exhaust pipe must be ≥ 3 meters from other building openings.Click here to type a system message.