18.4 Grease Ducts, Live Loads, Rigging & Mechanical Equipment

18.4 Grease Ducts, Live Loads, Rigging & Mechanical Equipment

The last Trade Area A cluster in this chapter is grease-handling ducts (filters, fans, fire and building codes), live loads, unloading and lifting, rigging, and mechanical equipment as it meets fire codes, sprinklers, and standpipes. The 2026 list gives you NFPA 96 2021, FBC Mechanical 2023 Chapter 5, and OSHA 29 CFR 1926 (July 1, 2025 edition). F.S. 489.105 again draws the license line: HVAC Class A/B may build the hood exhaust that the mechanical code assigns to the HVAC contractor; they may not install the standpipe or the sprinkler system they must keep clear of.

Quick Answer: Type I grease ducts are 16-gage steel or 18-gage stainless, liquid-tight welded, sloped 1/4 inch per foot (1 inch per foot if the horizontal run is over 75 feet), 18 inches off combustibles, and at least 500 fpm. Makeup air matches exhaust. Suppression shuts fuel and power to the appliances. Rigging is tagged, inspected each shift, and never overloaded. Do not cap a sprinkler or run a standpipe on an HVAC ticket.

Grease ducts — NFPA 96 2021 and FBC Mechanical 2023

A Type I hood collects grease vapors and smoke. A Type II hood collects steam, heat, and odors without grease. Fryers, griddles, broilers, woks, and similar grease-producing appliances need Type I. A dishwasher or an oven that the code treats as non-grease may be Type II. Type I exhaust must be independent of other exhaust (toilet, dryer, HVAC return) except the limited same-story, same-room interconnect rules in 506.3.5, and it must not serve solid-fuel appliances on a shared duct unless the code’s solid-fuel provisions are met.

FBC Mechanical 506.3.1.1 (field-fabricated) grease ducts:

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

Factory-built grease ducts listed to UL 1978 follow the listing, not a shop snap-lock. Joints, seams, and penetrations are a continuous liquid-tight weld or braze on the external surface (506.3.2). Pittsburgh locks, screws through the wall, and “high-velocity HVAC duct with extra mastic” are not grease duct. Overlapping joints, when used, are telescoping or bell type, inside section uphill, overlap not more than 2 inches, ID difference not more than 1/4 inch, so grease can drain. Bolts, screws, and rivets shall not penetrate duct walls for supports (506.3.3); hang from the structure with noncombustible supports.

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, at least 12 inches long and 1 inch deep, with a cleanout.

Clearance (506.3.6) where a rated enclosure is not used: 18 inches to combustible construction, 3 inches to noncombustible construction and gypsum on noncombustible structure. Listed ASTM E2336 wrap or UL 2221 factory enclosure can reduce clearance per the listing, not per a roll of ordinary duct wrap. Shafts are required when the duct penetrates a ceiling, wall, floor, or concealed space as 506.3.11 states.

Velocity (506.3.4): not less than 500 fpm in the grease duct (short transitions up to 3 feet are excepted if they cannot trap grease). Low velocity drops grease on the wall and turns the duct into fuel.

Cleanouts: openings only where needed for operation and maintenance; inaccessible sections get cleanouts not more than 20 feet apart and not more than 10 feet from changes of direction (506.3.8 / 506.3.9). Access panels in rated enclosures are labeled “ACCESS PANEL. DO NOT OBSTRUCT.” Before concealment, a light test with a lamp of not less than 100 watts must show every field weld liquid-tight (506.3.2.5).

Filters and fans. Grease-removal devices are listed grease filters (baffle-type as listed); residential mesh “range hood” filters are not a Type I installation. Exhaust fan motors shall be located outside the exhaust airstream (506.5.1.1). Housings are built as grease duct or listed to UL 762. Upblast fans serving Type I hoods are hinged, have a flexible weatherproof cable, have a restraint so the fan cannot flop off the roof, and the duct extends not less than 18 inches above the roof (506.5.4). Vertical discharge fans need a drain at the low point of the housing. Exhaust equipment still wants 18 inches to combustibles unless listed for less.

Termination (506.3.13): rooftop outlets not less than 40 inches above the roof. Generally 10 feet horizontally from adjacent buildings, property lines, and air intakes, or 3 feet above an intake; a 5-foot horizontal exception exists when discharge is directed away. Do not dump grease exhaust onto a walkway or into an HVAC outdoor-air intake.

Makeup air (508.1). Makeup shall be supplied while the kitchen exhaust runs; the amount from all sources shall be approximately equal to building exhaust. Mechanical makeup starts and operates simultaneously with the exhaust. 508.1.1: the temperature difference between makeup and the conditioned space shall not exceed 10°F unless the HVAC system can take the extra load. Drawings need an outdoor-air balance (508.1.2): replacement air equals exhaust plus net exfiltration.

Fire suppression (509.1 and NFPA 96). Appliances that require a Type I hood need an approved automatic fire suppression system (typically wet chemical, NFPA 17A, listed to UL 300). On actuation, fuel and electrical power to the protected appliances shut off. Makeup air typically stops so it does not feed oxygen; exhaust typically continues (or starts) to pull smoke and heat out. HVAC contractors install the hood, duct, fan, and makeup; they coordinate the suppression contractor — they do not “add two sprinkler heads in the hood” and call it a kitchen system.

Live loads, unloading, lifting, and OSHA 1926 rigging

Dead load is the weight of the structure and the permanently installed equipment. Live load is occupancy, maintenance, rain, and the people and tools on a roof or platform. A packaged rooftop’s operating weight on the schedule is a dead load the structure must already be designed for; a crane lift, a rolling RTU on 4×4s, and a loaded boom are construction loads you do not guess from the HVAC drawing. If the structural sheet does not support the scheduled 2,400-pound unit plus the 18-inch grease fan and a service live load on the platform, that is an RFI, not a Friday afternoon set.

OSHA 29 CFR 1926.251 (materials-handling rigging) is on the 2026 trade list:

• Inspect rigging prior to use on each shift and as needed during use (1926.251(a)(1)).
• Use only equipment with permanently affixed, legible identification markings showing the manufacturer’s recommended safe working load for the hitch and the angle it is based on, and the number of legs if more than one.
• Do not load a sling beyond the tagged working load.
• Remove from service if damaged, or if the tag is missing or unreadable. Remembered capacity is not a substitute.
• Alloy chain slings: size, grade, rated capacity, manufacturer. Wire-rope slings: size, hitch capacities, angle, legs. Synthetic slings: hitch capacities, fiber, legs.
• Job-made hooks and homemade chain are not a workaround.
• Protect slings from sharp corners; keep the load’s center of gravity under the hook; use tag lines to control the unit so it does not spin into a gas riser or a parapet.
• As sling legs spread, tension in each leg rises. A two-leg bridle that looks “almost flat” can be well above half the load per leg. Read the angle on the tag; industry practice keeps interior angles out of the dangerously flat range (often not below 30° from horizontal).

Cranes and derricks add Subpart CC: qualified operator, rated capacity, overhead power lines, and a lift plan. Forklifts on a roof are still powered industrial trucks with rated loads and fall hazards. Never stand under a live load. Unloading a 20-ton RTU at a Doral warehouse is the same standard as setting a 4-ton unit on a Naples strip-center roof: tagged slings, shift inspection, known weight from the schedule, known pick points, and a structure that can take the set.

Mechanical equipment, fire codes, sprinklers, and standpipes — know the HVAC limit

FBC Mechanical and the Florida Fire Prevention Code still apply to HVAC equipment: listed units, clearances, combustion air, grease exhaust, smoke detectors on large air handlers, fire and smoke dampers in rated assemblies. None of that turns an HVAC contractor into a fire-protection contractor.

• Automatic sprinklers are water-based fire protection under Chapter 633, F.S., not F.S. 489.105(3)(f) or (g). Do not install, relocate, cap, or “temporarily remove two heads that hit the curb.” Coordinate the conflict with the fire-protection contractor and the building official.
• Standpipes are listed in the mechanical contractor definition, F.S. 489.105(3)(i). They are not in Class A or Class B air-conditioning. Do not run a 2-1/2-inch standpipe drop “because we have the extra pipe.”
• HVAC must keep ducts, hangers, and equipment from obstructing sprinkler spray patterns and from loading standpipe risers. That coordination is a design/pre-install item: move the duct, not the head, unless the fire contractor relocates the head under a permit.
• Kitchen hood suppression is a listed pre-engineered or engineered special-hazard system (Section 509 / NFPA 96 / NFPA 17A), not a pair of ordinary sprinklers in the plenum.

Florida scenario. A certified Class A shop in Fort Lauderdale takes a restaurant TI: Type I hood, 16-gage welded grease duct rising two stories in a shaft, upblast UL 762 fan, 18 inches of duct above the roof, 40-inch discharge, 18-inch combustible clearance until the ASTM E2336 wrap begins, 1/4-inch-per-foot slope on a 40-foot horizontal, listed baffle filters, makeup RTU interlocked to start with the exhaust and within 10°F of space temperature. Suppression is a separate UL 300 contractor; on trip, gas and power to the fryers die, makeup stops, exhaust stays up. The same crane that sets the makeup RTU uses two-leg wire-rope slings with legible tags, inspected that shift, hooked at the manufacturer’s lift points, tag line on the corner. A sprinkler main crosses the proposed duct; the HVAC qualifier does not cut or cap it — the fire contractor relocates the main, and the duct is then welded and light-tested. A Class B qualifier could do a small Type I hood on a system within 25 tons / 500,000 Btu, but still could not install the boiler in the adjacent brew-pub, the pneumatic controls, or any portion of the sprinkler or standpipe.