Chapter 5 kitchen hoods, exhaust rates, grease duct, fire suppression, makeup air.
2
hours
0.2
CEUs
Codes and Standards
1.7.3
This course covers material relevant to the following ICC certification exams:
Chapter 5 kitchen hoods, exhaust rates, grease duct, fire suppression, makeup air.
Format
On-Demand Online
Delivery
Self-Paced
Access
24/7 After Enrollment
Certification
Certificate of Completion
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Contact our support teamDetermine appropriate hood type and calculate required exhaust rates
Kitchen exhaust gets its own dedicated set of provisions instead of being folded into general ventilation requirements because cooking produces byproducts that ordinary exhaust hardware was never built to handle safely. Grease-laden vapor, smoke, heat, excess moisture, and odor all leave the cooking surface together, and the first of those changes everything: grease is combustible residue, not simply an air-quality nuisance. Left to travel through standard ductwork, grease coats interior surfaces as it cools, and a coating of combustible residue inside a duct that also carries hot exhaust air is a fuel path waiting for an ignition source. That combination — a byproduct stream that is simultaneously a fire hazard and an indoor-air-quality problem — is why commercial kitchen exhaust is treated as its own subject rather than an extension of general ventilation rules.
That hazard profile is also what separates a Type I hood from a Type II hood, and the distinction turns entirely on what the cooking process actually produces, not on building type, kitchen size, or how upscale the operation looks. A Type I hood is the grease hood: built to work over equipment that generates grease-laden vapor or smoke, with grease-handling features and designed to integrate with a dedicated fire-suppression system, because the hazard it manages includes the possibility of an active fire inside its own exhaust path. A Type II hood removes only heat, steam, and moisture; it carries none of those features and cannot stand in for a Type I hood no matter how it is positioned over the equipment below. Whichever type applies, the hood's core job is the same: capture the effluent at the source and contain it within the hood-and-duct pathway rather than letting it escape into the room. A hood that fails to capture what it was sized to catch has failed at its primary function regardless of how correctly everything else was specified.
Picture a small café that has operated for years with only a coffee bar and countertop ovens, served by a single Type II hood sized for heat and moisture. The owner now wants to add a flat-top griddle and a countertop fryer to expand the breakfast menu, and the contractor's proposal simply extends the existing hood over the new equipment to save the cost of a second system. On paper the hood already covers the right footprint and the kitchen already has an approved exhaust system, which is exactly why this submittal is easy to wave through. The reviewer's job is to test that assumption against what the new equipment actually produces rather than against what is already installed: a griddle and a fryer generate grease-laden vapor, placing them squarely in Type I territory no matter how well the existing Type II hood performs its original job. Reusing the hood is not a minor substitution to negotiate — it is a mismatch between what the equipment produces and what the installed hardware can capture and contain.
The most common error at this stage is letting an existing hood's presence substitute for analysis of what the equipment underneath it actually produces — treating "there is already a hood here" as evidence of compliance rather than a question to be re-asked every time equipment changes. A related mistake is classifying hood type by the character of the establishment rather than the cooking process itself, assuming a coffee shop or bakery could not possibly need a Type I hood. Menu and equipment changes are especially easy to miss because they often arrive as a minor-looking permit revision long after the original hood was approved, with nobody revisiting the classification question the second time around. The correction is the same every time: go back to what the equipment produces, not what was previously approved or what the space is called, and confirm the installed hood matches what that classification requires.
Code Reference: IMC Chapter 5 - The code establishes minimum requirements for determine appropriate hood type to ensure public health, safety, and welfare. Requirements vary based on occupancy classification, construction type, and building height and area.
Apply grease duct and fire suppression system requirements
If the hood is where capture begins, the duct is where the hazard travels, and nothing else in the system carries the same combination of risk and consequence. Grease-laden air moving through a duct does not stay clean simply because the hood upstream is doing its job — vapor condenses and residue deposits on interior surfaces over the life of the system, and a duct lined with combustible residue is no longer ordinary sheet metal; it becomes a potential fuel path connecting the cooking line to whatever the duct passes through on its way out of the building. Construction has to answer directly to that reality. Seams and joints are welded rather than mechanically fastened, because a welded seam stays liquid-tight while a screwed or riveted one gives grease somewhere to pool and cure instead of draining continuously back toward the hood. The duct is sloped for the same reason, so accumulation trends toward a point where it can be managed rather than settling wherever gravity and geometry happen to leave it.
None of that matters if nobody can reach the inside of the duct once it is installed — cleanout openings at changes in direction and along straight runs exist because a duct that cannot be opened cannot be inspected or cleaned. Where the duct leaves the kitchen and travels through other occupied or concealed space, it needs protection from the building around it: enclosure in fire-rated shaft construction, or an alternative method actually tested and listed for grease-duct protection, plus clearance separating the duct from combustible material it passes near. A generic fire-rated wrap never evaluated for this application is not an equivalent substitute. Because the duct can carry an active fire rather than merely posing a risk, protection does not stop at construction — the hood, its plenum, the grease-removal filters, and the duct are covered together by a single automatic fire-extinguishing system, evaluated as one assembly. That system's interlock is what makes suppression a complete response: activation shuts down the fuel or electrical supply to the cooking equipment automatically, so a fire is not still being fed while an agent is discharged on top of it. A portable extinguisher rated for grease fires is a second line of defense for a person on scene — a backup to the automatic system, never a substitute for it.
During a rough-in inspection on a new restaurant buildout, the grease duct is still exposed above the ceiling grid — exactly the window in which its construction can be verified before it disappears behind finishes. Walking the run from hood to roof, the inspector finds several horizontal seams sealed with mechanical fasteners and a bead of sealant rather than continuously welded, and no cleanout where the duct turns to route around a structural beam. Continuing into the corridor the duct passes through on its way to the exterior, the duct is wrapped in an unlabeled insulation product with no documentation establishing it as a listed grease-duct protection system. At the hood, the automatic fire-extinguishing system is mounted and appears complete, but the wiring intended to shut off the gas supply to the cooking equipment on activation has not been connected to anything. Each finding is a variation on the same underlying problem: a piece of the assembly that looks finished but has not actually been built or connected to do the job it exists for.
Mechanically fastened seams are the most persistent construction error, usually because they look identical to a welded seam once wrapped, and the difference is only obvious to someone who inspects the joint directly. Missing or blocked cleanouts are a close second, often eliminated during coordination with structural framing without anyone reintroducing them once the conflict is resolved. Enclosure is frequently addressed with a general fire-rated product rather than one specifically tested and listed for grease-duct protection — an easy substitution to miss, since both can look similar once installed. Suppression failures tend to be about completeness rather than absence: hardware is mounted and cylinders are in place, but interlock wiring to the fuel or electrical supply was never finished, leaving a system that looks operational but would not actually shut down the equipment it protects. The fix is the same discipline applied consistently — verify the specific detail, not the general impression the installation gives at a glance.
Code Reference: IMC Chapter 5 - The code establishes minimum requirements for grease duct to ensure public health, safety, and welfare. Requirements vary based on occupancy classification, construction type, and building height and area.
Calculate and provide appropriate makeup air for kitchen exhaust systems
Every volume of air a kitchen exhaust hood removes has to come from somewhere, and makeup air is the system that supplies it. Without a properly balanced supply, the kitchen runs negative relative to the rest of the building: doors become noticeably harder to open, nearby fuel-burning appliances can struggle to vent properly, and the exhaust hood itself can lose the capture-and-containment performance the earlier modules built toward, because a hood pulling against an unbalanced room no longer behaves the way it was sized to. Volume is only part of the equation; where and how makeup air enters the room matters just as much. Air introduced too close to the hood face, or aimed directly at it, disturbs the thermal plume rising off the cooking equipment that the hood relies on to draw effluent upward and hold it inside the capture zone, and disturbed air can push grease-laden vapor and smoke back out into the room instead of into the hood.
Design responses include supplying a portion of makeup air from within the hood assembly itself, and placing diffusers or supply plenums away from the capture zone so incoming air reinforces the hood's performance instead of fighting it. The exhaust fan and the makeup air system are interlocked so the two run as a pair, including responding appropriately if the fire-extinguishing system activates rather than continuing to feed the space uncontrolled. Everything the earlier modules cover — correct hood classification, welded and sloped ductwork, cleanout access, a complete and interlocked suppression system — describes a system as it exists on the day it passes inspection, and none of it stays true automatically. Grease continues accumulating in the filters, the hood interior, and the duct for as long as the equipment underneath is in use, and only a maintained cleaning schedule keeps that ongoing accumulation from becoming the exact hazard the construction requirements exist to prevent. Plan review and initial inspection confirm a system is capable of being cleaned; whether it is actually cleaned on schedule is a question that only shows up later, in routine field inspection and, often, in a complaint.
An inspector responds to a complaint at an established restaurant: staff report the front entrance has become difficult to pull open during the dinner rush, and customers near the open kitchen have started asking about the haze hanging near the hood during busy periods. The inspection starts at the hood and works outward. The makeup air fan is running, but a damper linkage has come loose and the fan is delivering only a fraction of its intended airflow — the kitchen has been operating in negative pressure long enough that staff assumed the sticky door was just normal wear. Behind an access panel, grease has visibly built up around a cleanout that clearly has not been opened in a long time, thick enough that it is starting to bridge across the opening. Near the exit, a stack of stored supply boxes has been pushed against the wall directly below the fire-suppression system's manual pull station, leaving it effectively unreachable in an emergency. None of these findings would have been caught by a glance at the hood from across the kitchen, and none is unrelated to the others — an underperforming makeup air system, an unmanaged grease duct, and a blocked emergency device are the same underlying failure showing up in three places: a system that was allowed to drift out of the condition it was inspected in.
Undersized or disrupted makeup air is easy to miss because its symptoms — a stubborn door, a faint haze, a kitchen that feels warmer than it should — are gradual and easy to attribute to something else, rather than traced back to an exhaust-and-makeup-air imbalance. Supply diffusers aimed at or positioned too close to the hood face create the same capture failure through the opposite mechanism, disrupting the thermal plume instead of failing to replace enough air. On the maintenance side, the most common failure is not a construction defect at all but a simple absence of follow-through: cleanouts that were installed correctly and passed inspection go unopened for long stretches because cleaning is scheduled loosely or skipped when the kitchen is busy. Emergency equipment being physically blocked by storage or later renovations is a related pattern — the device still exists and would still show up on a checklist, but access to it has quietly disappeared. The correction across all of these is ongoing verification, not a one-time construction check.
Code Reference: IMC Chapter 5 - The code establishes minimum requirements for calculate to ensure public health, safety, and welfare. Requirements vary based on occupancy classification, construction type, and building height and area.
Commercial kitchen exhaust succeeds or fails as one connected system, not a set of independent components. It starts with a classification decision — matching hood type to what the cooking equipment actually produces — because that choice determines whether grease-handling and fire-suppression features belong in the design at all. From there, the grease duct carries the hazard physically through the building, which is why its construction, accessibility, enclosure, and integration with an automatic fire-extinguishing system are treated as a single evaluated assembly rather than separate checklist items. Makeup air closes the loop by keeping the whole arrangement in balance, supplying what the hood removes without undermining the capture it depends on. None of it is a one-time achievement: a system classified, built, and balanced correctly on the day of final inspection still depends on ongoing cleaning and maintenance to stay that way, and the failures that matter most in the field are as often about drift and neglect as they are about original construction. Reviewing and inspecting this system well means tracing that full chain every time — hood type, duct integrity, suppression integration, and air balance — rather than confirming any single piece in isolation.