Guide
Horizontal duct runs and access panel spacing
Long horizontal grease ducts fail cleans when elbows have no doors and straights stretch farther than a tool can reach. This page is about horizontal runs and spacing rules — direction changes, the secondary ≤12 ft opening interval, personnel-entry size, and high openings. It does not replace the broader missing panels / contractor questions guide. For multi-story shafts that crews skip, use vertical duct sections that get skipped.
Short answer
Secondary sources republishing NFPA 96 (2024 ed.) require openings at the sides or top of the duct (whichever is more accessible) and at changes of direction. On horizontal ducts, at least one 20×20 in opening for personnel entry where size allows; where that size is not possible, openings large enough for thorough cleaning at intervals not exceeding 12 ft (3.7 m). High openings not reachable from a ~10 ft stepladder need safe access / a work platform. Panels must be grease-tight and restored after service. Walk the run before you bid; put gaps and inaccessible lengths on the report. Your AHJ’s adopted edition wins.
Secondary spacing rules for horizontal grease duct (verify edition)
| Requirement (secondary excerpt) | Operator check on the run |
|---|---|
| §7.3.1 — openings at sides or top (whichever more accessible) and at changes of direction (HoodFilters / UpCodes IMC §510.3) | Every elbow, offset, and horizontal-to-vertical transition has a usable door — or is named inaccessible |
| §7.4.1.1 — on horizontal ducts, at least one 20 in × 20 in (508×508 mm) opening for personnel entry | Where the duct is large enough, is there a true entry opening — not only tiny cleanouts? |
| §7.4.1.2 — where 20×20 is not possible, openings large enough for thorough cleaning at 12 ft (3.7 m) intervals | Measure long straights; gaps >12 ft between usable doors are a spacing red flag (secondary) |
| §7.4.1.3 — if not easily accessible from a 10 ft (3 m) stepladder, openings need safe access and a work platform | Ceiling chase panels over a dining room that no one can stand at do not count |
| §7.1.6 (IMC mirror) — sign on access panels: ACCESS PANEL — DO NOT OBSTRUCT | Doors buried behind storage or other trades fail the usable-access test even if installed |
| §7.4.3 — same material/thickness as duct; gasket/sealant rated 1500°F (816°C); grease-tight; fasteners not penetrating duct walls; listed doors per listing | Sheet-metal “lids” and HVAC return doors are not grease-duct access doors |
UpCodes IMC §510.3.3 restates the 20×20 / 12 ft / stepladder language and cites NFPA 96:7.4.1.x. Some vendor pages compress section numbers differently — prefer HoodFilters / UpCodes wording, then confirm against the edition your AHJ adopts. We do not invent alternate spacing numbers.
Walk the horizontal run — what gaps look like
| Situation | What usually fails | Operator move |
|---|---|---|
| Direction change with no door | Elbow grease never reached from either end | Require a grease-tight door at the turn, or mark the corner inaccessible on the report |
| Long straight >12 ft, no cleaning openings | Middle of the run never brought to bare metal | Add openings on the secondary ≤12 ft interval (or personnel entry if size allows) |
| High opening, no platform | Door exists on drawings but is not usable from a 10 ft ladder | Safe access / work platform before calling it “accessible” |
| Damper in collar, no nearby door | Secondary language also expects access within ~18 in of hood dampers when not reachable under the hood | Confirm damper access separately from straight-run spacing |
| Fan with duct both sides | Older / secondary primers: access within ~3 ft each side of the fan | Coordinate with hinge / fan access — duct doors ≠ fan hinge |
Bid / report language that helps
- “Horizontal run length and every direction change listed; doors present or missing noted”
- “Where 20×20 not possible: cleaning openings ≤12 ft apart (secondary) or inaccessible length named”
- “Photos through each opened horizontal door; panel tags affixed”
- “Grease-tight / listed doors — not HVAC lids; restore gaskets after service”
- “Panel install priced separate from the clean”
Patterns that leave horizontal grease in place
- Canopy price only — no run length or elbow count on the quote
- “We’ll clean what’s accessible” with no map of the horizontal path
- Assuming one door at the hood cleans a 40 ft chase
- Blocked “ACCESS PANEL — DO NOT OBSTRUCT” doors treated as cleaned
- Confusing a return-air door with a grease-duct access door
Operator checklist for horizontal spacing
- Sketch the run — hood collar → elbows → long straights → riser or fan. Mark each turn.
- Measure straights — note any span without a usable cleaning opening past the secondary 12 ft interval.
- Check height — can a tech reach each door from a ~10 ft stepladder, or is a platform required?
- Clearance — pipes, cable trays, and storage in front of doors: who moves them?
- Panel quality — grease-tight, duct-equivalent / listed; fire-rated where the chase requires it (see fire-rated install notes in Sources).
- Proof — path photos + inaccessible lengths + panel locations on the written report within the two-week window.
- Vertical interface — horizontal-to-vertical transition is a high-load corner; do not leave it to the “riser later” excuse — see vertical sections.
Field note — spacing is not a canopy problem
- A shiny canopy does not prove elbows and long straights were opened. Demand duct-path photos, not only hood shots — same standard as bare metal clean and full-system vs canopy.
- Secondary trade explainers (Facilitec) stress that “cleaned everything accessible” without installing required openings leaves the operator holding the accessibility failure — not a finished clean.
- Complete Kitchen Exhaust and similar install pages frame openings at direction changes and at intervals not exceeding 12 ft; treat their section numbering as secondary and verify against HoodFilters / UpCodes / your adopted edition.
- No affiliate partnership on panel brands here. Ask for listed grease-duct doors sized to the opening and chase rating.
Who it’s for / not for
- For: GMs and facilities leads bidding kitchens with long ceiling chases; anyone whose last report never listed horizontal panel locations; operators after a deficiency about inaccessible duct
- Not for: DIY cutting into grease duct without a qualified installer / AHJ path; inventing spacing numbers beyond secondary cites; treating HVAC doors as grease-duct access
Sources
- HoodFilters — NFPA 96 excerpts (2024) (secondary; §4.1.8; §7.3.1 direction changes; §7.4.1.1–7.4.1.3 20×20 / 12 ft / stepladder)
- UpCodes — Exhaust duct systems (IMC 510) (code text mirror; §510.3 openings; §510.3.3 horizontal 20×20 / 12 ft / work platform; panel construction)
- Facilitec Southwest — access panel rule explained (secondary; direction changes; ~12 ft industry practice framing; “everything accessible” loophole)
- Complete Kitchen Exhaust — fire-rated access panel installation (secondary; 12 ft / direction-change framing — verify section numbers against current edition)
- US Made Supply — NFPA 96 access summary (secondary; 20×20, ≤12 ft, blocked cleanouts)
- Phil Ackland — need for proper access (PDF) (secondary / older edition citations; 12 ft + direction changes)
Next step
Walk or photo the horizontal path. Mark every direction change and every straight longer than the secondary 12 ft opening interval with no usable door. Put that sketch in the bid package, require inaccessible lengths on the report, and price grease-tight panel installs separate from the clean.