19.4 Kitchen Hoods, Exhausts & Drain Pans

19.4 Kitchen Hoods, Exhausts & Drain Pans

The last Trade Area B cluster is kitchen hoods, kitchen hood exhausts, and drain pans. Chapter 18.4 already covered grease-duct design, live loads, and rigging. This section is shop fabrication of the hood and the exhaust, plus the condensate pans FBC Mechanical 307 requires on every cooling coil that can wet a building. The 2026 list gives you NFPA 96 2021, FBC Mechanical 2023 Chapters 3 and 5, and SMACNA only as the comfort-duct book — do not build a Type I riser like a 2-inch-class supply.

Quick Answer: Type I hoods catch grease and smoke: FBC 507.2.3 steel 0.0466 in. (18 gage) or stainless 0.0335 in. (20 MSG), canopy 6 inches past the cooking surface, 18 inches off combustibles. Grease duct is 16-gage steel or 18-gage stainless, liquid-tight external weld, sloped 1/4 in/ft (1 in/ft if horizontal > 75 ft). FBC cleanouts: 20 ft horizontal, 10 ft from >45° turns; NFPA 96 is the 12 ft book. Makeup air ≈ exhaust (FBC 508). Drain pans: 3/4-inch pipe, 1/8 in/ft, plus a 307.2.3 overflow method.

Type I vs Type II hoods — what the shop builds

A Type I hood is required where appliances produce grease or smoke. Fryers, griddles, broilers, woks, and similar cooklines are Type I. If any appliance under a single hood needs Type I, the entire hood system is Type I (FBC 507). A Type II hood takes heat, steam, and odors without grease — many dishwashers and some ovens. You do not “upgrade” Type II with extra mastic and call it Type I.

FBC Mechanical 2023 Section 507.2.3 (Type I materials): steel not less than 0.0466 inch (No. 18 gage) or stainless steel not less than 0.0335 inch (No. 20 MSG). Listed factory-built hoods (UL 710) follow the listing. NFPA 96 2021 states hood steel not less than 0.043 in. (18 MSG) or stainless 0.037 in. (20 MSG) — same idea, slightly different gage tables. On CBT, open the book the stem names. Field-welded joints in the hood canopy are liquid-tight, continuously welded, with the interior ground so grease does not sit on a weld bead.

Canopy size (FBC 507): a canopy-type hood shall extend a horizontal distance of not less than 6 inches beyond the edge of the cooking surface on all open sides. Island canopies hang over all four sides; wall canopies overhang the front and ends. Proximity / backshelf / pass-over hoods are listed devices with their own capture envelopes — you do not short the 6-inch canopy rule by calling a canopy a backshelf. Distance from canopy to cooking surface is limited (commonly not more than 4 feet on canopy hoods). Each exhaust outlet typically serves not more than a 12-foot section of hood — long cooklines get multiple ducts or a listed manifold.

Clearance: a Type I hood is installed with not less than 18 inches to combustibles (FBC 507.2.6), unless a listed clearance-reduction system or the hood listing says otherwise. Ordinary duct wrap is not an 18-inch substitute.

Grease filters: listed baffle filters (UL 1046 when they are removable and not integral to a listed hood). Installed at not less than 45 degrees from horizontal so grease drains to a trough, not onto the cook. Mesh filters standing alone are not the Type I grease-removal device. Filters must be removable for cleaning; a shop-welded mesh screen is not a filter.

Fire suppression (FBC 509 / NFPA 96 / UL 300 wet chemical) is a listed system that covers the appliances, the hood plenum, and the duct. HVAC fabricates the hood and the duct openings the suppression contractor needs; you do not substitute a portable extinguisher for a UL 300 plenum nozzle. On actuation, fuel and power under the hood shut down.

Kitchen hood exhausts — continuity, slope, cleanouts, makeup air

Type I exhaust shall be independent of other exhaust (toilet, dryer, HVAC return) except the narrow same-story exceptions in 506.3.5. It shall not be 26-gauge snap-lock with foil tape.

Field-fabricated grease duct (FBC 506.3.1.1 / NFPA 96):

• Carbon steel not less than 0.0575 inch (No. 16 gage), or
• Stainless steel not less than 0.0450 inch (No. 18 gage)

Joints, seams, and penetrations: continuous liquid-tight weld or braze on the external surface (506.3.2). Factory-built grease duct listed to UL 1978 follows the listing. Bolts, screws, and rivets shall not penetrate duct walls for supports (506.3.3). Overlapping joints, when used, are telescoping or bell type, inside section uphill, overlap not more than 2 inches, so grease drains.

Slope (506.3.7): not less than 1/4 unit vertical in 12 horizontal (2 percent) toward the hood or an approved grease reservoir. Where horizontal ducts exceed 75 feet, slope not less than 1 unit vertical in 12 (8.3 percent). No dips or traps. Reservoirs, when used, are built as grease duct.

Velocity: not less than 500 fpm in the grease duct (short transitions excepted if they cannot trap grease).

Clearance (506.3.6) where a rated enclosure is not used: 18 inches to combustibles, 3 inches to noncombustible. Listed ASTM E2336 wrap or UL 2221 factory enclosure can reduce clearance per the listing.

Cleanouts — two books, two spacings. This is a classic open-book trap.

If the stem says Florida Building Code Mechanical, use 20 feet / 10 feet. If the stem says NFPA 96, use the 96 access table (the stricter 12-foot horizontal tradition). Do not invent a third number.

Fans: Type I exhaust fans keep the motor out of the airstream, listed for grease (UL 762) or built as grease duct. Upblast rooftop fans are hinged with a grease trough, and FBC wants on the order of 18 inches of duct above the roof under that fan so the hinge works and grease does not dump at the curb. Makeup air (FBC 508) shall be supplied during exhaust operation, approximately equal to exhaust, interlocked to start with the exhaust, and shall not reduce capture. Short-circuit compensating air dumped inside the canopy is limited by listing and by the code’s “shall not reduce effectiveness” rule — it is not a license to starve the hood. Makeup ducts within 18 inches of a Type I hood are built to the grease-adjacent rules in 506, not as ordinary flex. Domestic hoods over 400 cfm need makeup air too (505.2), with closure and automatic start.

Worked example. A 10-foot wall canopy over a fryer-griddle line in a Tampa strip center: stainless Type I, 6-inch front and end overhang, listed baffles at ≥ 45°, one duct outlet (hood ≤ 12 ft), 16-gage welded riser sloped 1/4 in/ft back to the hood on a 40-foot horizontal, cleanouts at the 90° and at ≤ 20 ft (FBC) along the run, 500 fpm minimum, 18 inches off wood trusses or listed wrap, upblast fan hinged, makeup air interlocked and roughly equal to exhaust. Substituting 22-gauge HVAC spiral with mastic is every wrong row of that table.

Drain pans — FBC Mechanical 307

Every evaporator and cooling coil that actually condenses needs a drain pan and a drain (307.2). Florida latent loads make this a weekly service item; the exam still wants the code pan, not a leftover cookie sheet.

Primary drain (307.2.1 – 307.2.2):

• Convey condensate from the pan outlet to an approved place of disposal.
• Horizontal slope not less than 1/8 in/ft (1 percent).
• Pipe not less than 3/4 inch and shall not decrease toward the disposal point.
• Table 307.2.2 (manifolded units): up to 20 tons → 3/4 in.; 20–40 tons → 1 in.; 40–90 tons → 1-1/4 in.; 90–125 tons → 1-1/2 in.; 125–250 tons → 2 in. Class B’s 25-ton cap sits on the 1-inch row once you manifold over 20 tons.
• 307.2.1.1: condensate drains shall not directly connect to plumbing DWV. They may discharge to a floor sink, floor drain, trench drain, mop sink, hub drain, standpipe, utility sink, or laundry sink. F.S. 489.105 lets Class A/B run condensate to an existing safe waste, not a new sanitary system.
• Trap as the manufacturer requires (307.2.4). Mini-splits: inline check valve or a trap (307.2.4.1). Configure the line so you can clear it without cutting (307.2.5). Attic condensate pumps shut the equipment down on pump failure (307.3).

Overflow — 307.2.3. Where overflow could damage building components, provide one of:

1. Auxiliary drain pan with a separate drain to a conspicuous point. Pan not less than 1-1/2 inches deep, not less than 3 inches larger than the unit or coil in width and length, corrosion-resistant. Galvanized not less than 0.0236 in. (No. 24 gage); nonmetallic not less than 0.0625 in.
2. Separate overflow drain from the equipment pan, connected higher than the primary, to a conspicuous point.
3. Auxiliary pan without a drain, with a UL 508 water-level device that shuts the equipment off before overflow. Pan built as Item 1.
4. UL 508 device in the primary drain line, the overflow line, or the equipment pan, higher than the primary connection and below the overflow rim.

307.2.3.1 (downflow and coils with no secondary pan provision): the water-level device goes inside the primary drain pan. Devices installed in the drain line shall not be permitted on those units. 307.2.3.2: equipment and insulation that would be damaged sit above the rim of the auxiliary pan; supports in the pan are water-resistant. Mark concealed primary vs secondary terminations (307.2.3.3).

Shop-fabricated auxiliary pans are 24-gage galvanized (or listed plastic), 1-1/2 inches deep, 3 inches larger all around, with a 3/4-inch drain fitting if Item 1 is the method, sloped to that fitting. A pan that is 24 gage but flat under a 60-inch coil, with no drain and no float, is not a 307.2.3 method.

Florida HVAC scenario

A certified Class B shop in Miami-Dade hangs a 5-ton air handler in a second-floor closet over finished space and, on the same permit set, a Type I hood in the first-floor café (5 tons is under 25; the hood is still Trade B). The air handler gets a 24-gage auxiliary pan 3 inches larger, 1-1/2 inches deep, with a 3/4-inch secondary run to a conspicuous wall, plus the primary 3/4-inch at 1/8 in/ft to a hub drain — not glued into the sanitary stack (307.2.1.1). The Type I hood is 20 MSG stainless, 6-inch overhang, baffles at 45°, welded 16-gage riser sloped 1/4 in/ft, FBC cleanouts on the 20-foot rule, makeup air interlocked. The helper wants to snap-lock the grease riser “because it is only 14 inches, under 2 feet.” Under-2-foot SMACNA HVAC tables do not apply to Type I exhaust. Two Trade B items, two books: 307 for the pan, 506/507/508 plus NFPA 96 for the hood.

Traps: (1) 26-gauge Pittsburgh grease duct. (2) Using FBC’s 20-foot cleanout spacing on an NFPA 96 question (or 12-foot on an FBC-only stem). (3) Zero overhang on a canopy. (4) Auxiliary pan that is smaller than the unit. (5) Drain-line float on a downflow coil (307.2.3.1). (6) Condensate glued into the sanitary tee. (7) Makeup air not interlocked.