Commercial Kitchen Ventilation Guide: How Exhaust Systems Work

A commercial kitchen ventilation system does more than just remove smoke. It captures grease-laden vapors, reduces fire risk, maintains air quality, controls temperature, and keeps your kitchen compliant with NYC building and fire codes. Understanding how the system works helps you maintain it properly and recognize problems before they become expensive.

This guide covers every component of a commercial kitchen exhaust system, how they work together, and what you need to know about maintenance.

The Exhaust System: An Overview

A commercial kitchen ventilation system has five primary components that work as a connected system:

1. Exhaust hood — captures contaminated air above the cooking line
2. Grease filters — remove grease particles from the airstream
3. Ductwork — carries contaminated air from the hood to the exterior
4. Exhaust fan — creates the negative pressure that drives airflow
5. Makeup air unit — replaces exhausted air with fresh air

Air flows in one direction: from the cooking surface, through the hood and filters, through the ductwork, and out through the fan on the roof. Makeup air flows into the kitchen to replace what was exhausted. When every component is working correctly, the kitchen stays clear, comfortable, and safe.

Component 1: The Exhaust Hood

The hood is the most visible part of the system — the stainless steel canopy above your cooking equipment.

Type I Hoods (Grease Hoods)

Required for all cooking equipment that produces grease-laden vapors:

• Grills and charbroilers: Produce the highest volume of grease vapors
• Deep fryers: Generate significant grease-laden steam
• Ranges and cooktops: Open-flame cooking produces grease vapor and combustion byproducts
• Ovens (particularly convection and high-temperature): Generate grease vapor during roasting and baking
• Wok ranges: Extremely high heat produces intense grease-laden vapor

Type I hoods include grease filtration, connect to fire-protected ductwork, and must have an automatic fire suppression system. They are governed by NFPA 96.

Type II Hoods (Heat and Moisture Hoods)

Required for equipment that produces heat, steam, or moisture but not grease:

• Dishwashers
• Steam tables and kettles
• Pasta cookers
• Ovens used only for baking (no animal fats or oils)

Type II hoods are simpler — they do not require grease filters, fire suppression, or the same level of ductwork protection. They are not subject to NFPA 96 cleaning requirements.

Hood Design Factors

The hood must be sized correctly for the cooking equipment beneath it. Key factors include:

• Overhang: The hood must extend beyond the cooking surface on all open sides (typically 6 inches minimum on front and sides)
• Height: Mounting height above the cooking surface affects capture efficiency — too high and vapors escape, too low and it interferes with cooking
• Airflow volume: Measured in cubic feet per minute (CFM), the hood must capture all grease-laden vapors at the cooking surface
• Construction: Minimum 18-gauge stainless steel, with all joints liquid-tight to contain grease

Component 2: Grease Filters

Grease filters sit in the hood opening and are the first line of defense. As air passes through them, they capture grease particles through various mechanisms.

Baffle Filters

The most common type in commercial kitchens. Air is forced through a series of baffles (angled plates) that cause grease particles to change direction rapidly. The grease cannot follow the sharp turns and instead collects on the baffle surfaces, draining down into the grease trough.

Advantages: Durable, effective, easy to clean, long lifespan Maintenance: Should be cleaned by kitchen staff weekly — soak in hot water with degreaser, scrub, and air dry

Mesh Filters

Less common in modern commercial kitchens. Multiple layers of mesh screen trap grease particles.

Advantages: Lower cost Disadvantages: Clog faster, less effective at high temperatures, harder to clean, more fire risk Maintenance: Must be cleaned more frequently than baffle filters

Filter Maintenance

Regardless of type, filter maintenance is your staff’s responsibility between professional cleanings:

• Remove filters at least weekly (daily in high-volume kitchens)
• Soak in hot water with commercial degreaser
• Scrub to remove stubborn grease
• Rinse thoroughly and allow to dry completely before reinstalling
• Install in the correct orientation — filters are designed to drain grease in one direction
• Replace damaged filters immediately — warped or cracked filters leave gaps that allow grease to bypass filtration

Component 3: Ductwork

Ductwork connects the hood to the exhaust fan, carrying grease-laden air through the building to the roof. It is the most fire-critical component of the system.

Construction Requirements

NFPA 96 and NYC building codes specify:

• Material: Minimum 16-gauge carbon steel (welded) or 18-gauge stainless steel. No screws — only continuous welds. Screws create grease collection points and can allow leaks
• Joints: All joints welded and liquid-tight
• Slope: Horizontal runs must slope back toward the hood (or toward an approved drain) so grease does not pool in the duct
• Clearance: Minimum 18 inches from combustible materials (reduced to 3 inches with specific insulation methods)

Access Panels

Access panels are required at every change of direction (elbows, tees) and at intervals along straight runs. They serve two purposes:

1. Cleaning access: Without access panels, technicians cannot reach the inside of the duct to clean it
2. Inspection access: The FDNY needs to be able to see inside the ductwork during inspections

Missing access panels are one of the most common code violations in older NYC buildings. If your ductwork was installed without adequate access, you should have panels added. The cost of retrofitting access panels is far less than the cost of FDNY violations or a duct fire.

Common Ductwork Issues in NYC

Older buildings in Manhattan present unique ductwork challenges:

• Shared chases: Multiple tenants’ ductwork may run through the same vertical chase, creating cross-contamination and fire spread risks
• Long horizontal runs: Kitchens in basements or the middle of buildings require long duct runs that accumulate more grease
• Tight spaces: Ductwork routed through narrow cavities makes cleaning difficult
• Legacy installations: Older ductwork may not meet current code for material, construction, or clearance

Component 4: The Exhaust Fan

Located on the rooftop in virtually all NYC installations, the exhaust fan creates the negative pressure that drives airflow through the entire system.

How It Works

The fan pulls air from the kitchen, through the hood and filters, through the ductwork, and exhausts it above the roofline. The fan must be powerful enough to create sufficient airflow (measured in CFM) to capture all cooking vapors at the hood.

Fan Types

• Upblast fans: The most common type for commercial kitchens. They exhaust air upward, away from the roof surface. This is preferred because it disperses grease-laden exhaust away from the building
• Utility set fans: Used when ductwork configuration requires a different fan arrangement

Fan Maintenance

The exhaust fan requires regular attention:

• Professional cleaning at each hood cleaning interval — the fan is part of the system
• Belt inspection: V-belt drive fans need belt tension and wear checked regularly
• Bearing lubrication: Per manufacturer specifications
• Grease containment: The catch pan or drain must be emptied and cleaned regularly
• Motor condition: Listen for unusual noise and check for excessive vibration

A failing exhaust fan reduces airflow, which means the hood cannot capture vapors effectively. The result: grease accumulates in the kitchen instead of being captured by the exhaust system, increasing both fire risk and sanitation issues.

Component 5: Makeup Air

When the exhaust system removes air from the kitchen, that air must be replaced. Without makeup air, the kitchen operates under negative pressure, which causes a cascade of problems.

Why Makeup Air Matters

• Exhaust efficiency: A kitchen under excessive negative pressure does not allow the exhaust fan to work at full capacity. The fan struggles to pull air through the ductwork
• Door behavior: Doors become hard to open (pulling against negative pressure) or slam shut violently
• Comfort: Uncontrolled air enters through every gap — around doors, windows, and through the building envelope. In winter, this means cold drafts. In summer, hot and humid air
• Cross-contamination: Uncontrolled air intake can pull odors, dust, and pests from unexpected locations

Makeup Air Units (MAU)

A properly designed makeup air system provides:

• Tempered air: Heated in winter, cooled in summer, so the replacement air does not create temperature extremes
• Filtered air: Outside air is filtered before entering the kitchen
• Controlled distribution: Air is distributed through supply diffusers positioned to avoid disrupting the exhaust hood’s capture zone
• Balance: The MAU is matched to the exhaust volume to maintain neutral or slight negative pressure

Signs of Inadequate Makeup Air

• Doors are difficult to open or slam shut
• The hood does not seem to capture smoke and vapors effectively
• The kitchen is excessively hot or cold
• You hear whistling at door and window seals
• Grease is accumulating on surfaces far from the cooking line

Maintaining the Complete System

Every component of the ventilation system requires maintenance. Neglecting any single component affects the entire system’s performance.

Your Staff’s Responsibilities

• Clean grease filters weekly (or daily in high-volume kitchens)
• Wipe down the hood exterior during daily cleaning
• Report any changes in airflow, unusual noises, or visible smoke accumulation
• Keep the area around the hood and cooking equipment clean of grease

Professional Maintenance

• Hood and ductwork cleaning at NFPA 96 intervals
• Fan service at each hood cleaning
• Fire suppression system inspection every six months
• Makeup air unit filter changes and service per manufacturer schedule
• Annual system performance evaluation

For a detailed maintenance calendar, see our hood cleaning maintenance schedule guide.

Bottom Line

Your commercial kitchen ventilation system is an integrated machine. The hood captures, the filters separate, the ductwork transports, the fan drives, and the makeup air replaces. When every component is properly maintained, the system keeps your kitchen safe, comfortable, compliant, and productive.

The most important maintenance action is regular professional cleaning of the hood, ductwork, and fan at the frequency required by NFPA 96. Everything else supports that core requirement.

Need your ventilation system assessed? Contact Empire Hoods for a free evaluation of your entire exhaust system.