How Is Restaurant Exhaust Engineered in Mixed-Use Buildings?

The engineer matches the hood to the cooking line. Solid-fuel cooking, woks, and charbroilers produce the heaviest effluent and need the highest exhaust rates and often dedicated hood sections; lighter cooking needs less. The hood's exhaust rate is set per the code's formulas and the manufacturer's listing, and the engineer confirms the kitchen layout keeps the equipment under the hood's capture zone — a fryer rolled six inches past the hood edge is effectively unhooded. Compensating hoods that introduce tempered air at the hood reduce the load on the building's makeup-air system and are often worth the premium in cold or hot climates. Makeup air is sized to the exhaust, not to the kitchen's comfort. A commercial kitchen exhaust can move 4,000 to 10,000 cubic feet per minute; without replacement air, the kitchen pulls it from wherever it can — under doors, down the grease duct, from the residential corridors above. The engineer provides a dedicated makeup-air unit, tempered for the climate, interlocked with the exhaust fan so the two always run together, and distributes the makeup air to avoid blowing across the cooking line and disrupting capture. The kitchen is kept slightly negative to the dining room so odors stay in the kitchen, but neutral to the building so it never steals air from the residences.

The grease duct is built like a chimney because it is one. Welded black-steel construction with liquid-tight seams, cleanouts at each change of direction and at code-required intervals, pitched to drain grease back toward the hood or to a collection point — the engineer details all of it on the mechanical plans. The shaft enclosure carries the fire rating the code requires for the occupancy separation it passes through, and the engineer coordinates the shaft's location with the structural engineer early, since a two-by-two-foot rated shaft running five residential floors needs a home in the framing plans, not a field route. At the roof, the upblast fan discharges the effluent vertically at high velocity so the plume rises clear of the building. The engineer locates the fan per the code's clearance requirements — from the roof surface, from parapets, from air intakes and operable openings — and then goes further for mixed-use: checking the residential balconies, rooftop amenity decks, and operable bedroom windows against the prevailing wind rose. Odor filtration, where required, is placed for service access — carbon modules and precipitators need regular maintenance, and a filter bank buried behind equipment does not get serviced. The engineer writes the maintenance access into the roof plan.

Use this checklist before the kitchen exhaust design is finalized: • Type I hood sized and listed for the actual cooking equipment and its effluent class • Exhaust rate balanced with dedicated tempered makeup air, interlocked to run together • Welded grease duct in a fire-rated shaft, routed as directly as possible to the roof • Cleanouts at every change of direction and code-required intervals, with access shown • Shaft enclosure rated for every occupancy separation the duct passes through • Upblast fan listed for grease duty, terminating clear of intakes, windows, and balconies • Prevailing-wind study confirming the plume clears residential terraces and amenity decks • Odor filtration specified with fan static and maintenance access accounted for