Commercial Kitchen Exhaust System Components: Complete Design & NFPA 96 Guide 2026

Commercial Kitchen Exhaust System Components: Complete Design & Selection Guide 2026

Understanding how a commercial kitchen exhaust system works matters whether you are a restaurant owner reviewing a contractor quote, a facility manager overseeing a hood replacement, or a duct cleaning contractor who needs to know what you are cleaning. This guide explains every component of a Type I (grease) kitchen exhaust system, how they work together, and what NFPA 96 requires at each point.

Kitchen Exhaust System Overview: The Complete Flow Path

A commercial kitchen exhaust system is a continuous assembly from the cooking surface to the outdoors. Grease-laden air enters the hood at the cooking surface and travels through filters, ductwork, and the exhaust fan — with grease condensing and accumulating at every point along the way. A properly designed system captures 85-95% of cooking effluent at the hood. What does not get captured in the hood ends up in the ducts, where it becomes a fire hazard.

Component Breakdown

1. Exhaust Hood (Type I vs Type II)

Type I hoods are for grease-producing cooking: fryers, griddles, charbroilers, woks, and solid fuel (wood, charcoal). They are constructed of 18-16 gauge stainless steel (type 304 or 430) and include a grease capture system, drainage, and access for cleaning. Type II hoods are for heat, steam, and odor only: dishwashers, steam tables, ovens (non-grease-producing). They are lighter construction and do not require grease filters.

NFPA 96 requires all Type I hoods to have a listed grease removal device (baffle filter, cartridge filter, or water wash system) and access panels for cleaning the entire hood interior.

2. Grease Filters (Baffle, High-Velocity Cartridge, Water Wash)

• Baffle filters: The most common type. Stainless steel overlapping channels that force air to change direction, causing grease droplets to impinge on the metal surfaces and drain to a collection cup. Efficiency: 40-60% for typical cooking, dropping to 20-30% for high-grease operations like charbroiling
• High-velocity cartridge filters (HVCF): Also called "ultraviolet" or "precipitator" filters. Smaller, tighter baffling that achieves 70-90% grease removal. These are the filters that enable "grease duct without access panels" designs in some jurisdictions — but check local code before eliminating duct access
• Water wash / mist elimination: Integrated water spray system inside the hood that continuously washes grease from the hood interior. Common in high-volume chain kitchens. Reduces filter cleaning frequency but adds plumbing and water treatment complexity
• Electrostatic precipitators (ESP): Electrostatic charge captures sub-micron grease and smoke particles. 90-98% efficiency. High upfront cost but very low ongoing maintenance. Used where smoke and odor control are critical (mall food courts, open kitchens in dining rooms)

3. Grease Duct

The grease duct connects the hood to the exhaust fan. NFPA 96 specifies minimum 16-gauge carbon steel or 18-gauge stainless steel, continuously welded (no snap-lock seams), with liquid-tight joints sloped toward the hood for drainage. All grease ducts must be enclosed in a fire-rated shaft (1-hour or 2-hour rating depending on building construction type) with clearance to combustibles of at least 18 inches (or per the duct manufacturer's listing).

Key duct design rules:

• Minimum slope: 1/4 inch per foot toward the hood (or toward a grease reservoir)
• Duct velocity: 1,500-2,200 FPM (feet per minute) — too slow and grease condenses, too fast and noise becomes excessive
• Access for cleaning: NFPA 96 requires access panels every 12 feet of horizontal duct, at every change of direction, and at the duct-to-fan connection. Minimum opening size: 12" × 12" or the duct cross-section, whichever is larger
• No fasteners penetrating the duct interior (screws become grease collection points and ignition sources in a fire)

4. Exhaust Fan (Upblast vs Utility Set vs Inline)

Fan Type	Best For	Pros	Cons
Upblast roof fan	Most restaurants, 1-3 hoods	Simple, inexpensive, easy to service, throws exhaust up and away	Visible on roofline, requires roof penetration, grease drips onto roof if not maintained
Utility set fan	Large exhaust volume, long duct runs	High static pressure capability, belt-driven for speed adjustment	More expensive, requires separate grease drain, heavier (roof structure must support)
Inline fan	Interior duct routing, multi-story buildings	Acoustically isolated, no roof penetration, easy to service from inside	Requires interior mechanical room space, more complex duct layout

5. Makeup Air (MUA) System

Every CFM of air exhausted from the kitchen must be replaced — otherwise the building goes negative pressure, causing back-drafting from water heaters and boilers, doors that are hard to open, and outdoor air infiltrating through every gap. Commercial kitchens typically exhaust 2,000-10,000+ CFM, so makeup air is a major HVAC design element.

Makeup air strategies:

• Through the hood (short-circuit): MUA is introduced directly into or adjacent to the hood. Energy-efficient (conditioned air goes straight to exhaust), but less comfortable for cooks standing at the hood
• Displacement / low-velocity: MUA is introduced at floor level at low velocity. Tempered air rises naturally through the kitchen, providing a more comfortable work environment. Requires more ductwork and floor space
• Transfer air: Conditioned air from the dining room flows into the kitchen to serve as MUA. Reduces dedicated MUA equipment cost but transfers kitchen odors to the dining room if not carefully balanced

6. Fire Suppression System

Every Type I hood requires an automatic fire suppression system (ANSI/UL 300 listed). The system uses wet chemical agents that discharge over cooking appliances, into the hood plenum, and into the duct collar. All gas and electric cooking appliances under the hood must be interlocked to shut off upon system activation. Fire suppression systems must be inspected and serviced every 6 months by a licensed contractor.

NFPA 96 Design Documentation Requirements

NFPA 96 Section 5.1 requires that the exhaust system design be documented, including: hood dimensions, duct size and routing, fan selection (CFM and static pressure), makeup air strategy, and fire suppression coverage. This documentation is what the fire marshal reviews during plan check and what the hood cleaning contractor references to know exactly what they are working on.

Specifying or upgrading a kitchen exhaust system? Contact Gaolijie for exhaust cleaning equipment and technical support for your project.