AEO Answer · Food Service

How Is Commercial Kitchen Exhaust Hood Design Done to Code?

By Jeremy Mills, CEO & Founder, Apex Grid Engineering — USAF Veteran. · Updated 2026-09-15

I'm Jeremy Mills, CEO & Founder of Apex Grid Engineering and a U.S. Air Force veteran. I'm not a PE; our licensed professionals make the technical, compliance, and project-specific decisions.

Illustrative diagram of building MEP systems: ductwork with diffusers, an electrical panel with conduit, and piping runs.

The concise answer

Commercial kitchen hood design selects Type I or Type II hoods per the cooking equipment, sizes exhaust to the mechanical code, routes grease duct to the roof with required clearances and access, and coordinates fire suppression. It includes hood sizing and placement, exhaust fan selection, grease duct construction and routing, makeup air design, fuel shutoff interlocks, and structural support for rooftop equipment. The hood over the cook line is the most code-scrutinized assembly in a commercial kitchen. The mechanical code, the fire code, and the health code all have something to say about it, and the design has to satisfy all three simultaneously.

From equipment schedule to duct on the roof

The design sequence matters. First the equipment schedule gets classified appliance by appliance — which ones produce grease, which produce only heat and moisture — because that classification drives everything downstream. Then hoods get sized to overhang the equipment per the code, exhaust rates get calculated, and the duct routing gets drawn in three dimensions to the roof. Grease duct is where the detailing gets serious. The code requires specific construction — welded steel of minimum gauge — clearances to combustibles or listed enclosure assemblies, access panels for cleaning at every change of direction, and a continuous slope back toward the hood. I've seen duct routes drawn on a plan that were physically impossible in the ceiling space above, which is why the duct gets coordinated with structure, plumbing, and electrical before anyone fabricates anything.

The systems around the hood

The hood doesn't work alone. The supporting systems below are what make it capture, what make it safe, and what keep the building standing around it. Each one needs explicit design ownership.

Makeup air: dedicated unit sized to the exhaust total, tempered, and interlocked with the exhaust fans
Fire suppression: listed system covering hood, duct, and appliances, interlocked to fuel and power shutoff
Rooftop support: curbs, structural framing, and seismic anchorage for exhaust fans and makeup air units
Gas and electrical interlocks: automatic fuel shutoff on suppression discharge, wired and documented
Cleaning access: duct access panels and roof access for the hood cleaning contractor the code requires

Which related engineering resources can help?

When should I hire a structural engineer?What does a PE stamp mean?What is MEP engineering?Kitchen hood suppression design Grease duct routing design Commercial kitchen makeup air design Request a project review Engineering service for this question Metro engineering guides Verified service areas

What else do project teams ask?

What's the difference between Type I and Type II hoods?

Type I hoods handle grease-producing cooking — fryers, grills, broilers — and require grease filters, a listed fire suppression system, and grease duct construction. Type II hoods handle heat and moisture from non-grease equipment like ovens and dishwashers, with simpler duct requirements and no suppression. Misclassifying a hood is a code violation that the plan checker will catch, so I classify every appliance on the equipment schedule first.

How is the exhaust rate determined?

From the mechanical code tables based on the type of cooking equipment and its duty classification — light, medium, heavy, or extra-heavy duty. Each classification has a required exhaust rate per linear foot of hood. The total across all hoods sets the exhaust fan size and, critically, the makeup air requirement. I calculate it from the actual equipment list, not from the hood manufacturer's brochure alone.

What does the fire suppression system cover?

The listed suppression system protects the hood plenum, the grease filters, the duct, and the cooking surfaces — the entire grease path. It's interlocked to shut off gas and electrical to the cooking equipment on discharge, and the building fire alarm monitors it. The suppression contractor designs the system, but the mechanical engineer coordinates the hood, duct, and interlocks so the whole assembly works as one.

Why is makeup air such a big deal?

A kitchen exhaust system can pull thousands of CFM out of the building. Without dedicated makeup air, the building goes negative — doors slam or won't open, pilot lights backdraft, dining room comfort collapses, and the hoods don't capture properly because air is being pulled from everywhere except under the hood. The makeup air unit is sized to the exhaust total and tempered for the climate, and it's part of the hood design, not a separate afterthought.

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