Guide
Grease filter types: baffle vs mesh and why NFPA 96 cares
Kitchen managers often treat “hood filters” as one product. Code does not. Removable grease-removal devices for commercial cooking are expected to be listed, rigid, and installed so all exhaust air passes through them. Mesh pads that look like furnace filters fail that test as a standalone device. This page is the operator split: baffle vs mesh, what listing marks to check, and what to do when someone left the wrong type in the canopy.
Short answer
Secondary NFPA 96 (§6.1.1–6.1.3) requires listed grease filters or other listed grease-removal devices. Removable filters that are not an integral part of a listed hood must be listed to UL 1046 (or CAN/ULC-S649 in Canada). Mesh filters shall not be used unless they were evaluated as an integral part of a listed exhaust hood or listed together with a primary filter under UL 1046. Everyday Type I canopies use stainless baffle filters. Staff wash baffles on a volume-driven cadence; warped or unlisted stock gets replaced — see clean vs replace. Your AHJ’s adopted edition wins.
Baffle vs mesh
| Type | What it is | Code posture (secondary NFPA 96) | Operator action |
|---|---|---|---|
| Baffle | Rigid steel or stainless channels that force grease-laden air through turns so grease drains to a trough | Standard listed grease filter when marked UL 1046 / equivalent and installed per listing | Wash, dry, reinstall vertical; replace when warped, corroded, or unlisted |
| Mesh (standalone) | Wire / expanded-metal pad that traps grease in the mesh itself | §6.1.3: mesh not used unless integral to a listed hood or listed with a primary filter under UL 1046 | Replace with listed baffles unless the hood listing explicitly allows that mesh arrangement |
| Mesh + primary filter (listed pair) | Mesh evaluated only with a listed primary filter assembly | Allowed only when the UL 1046 listing covers that combination | Keep the listed primary filter in place; do not run mesh alone |
| Integral to a listed hood | Grease-removal device built into a UL 710 (or equivalent) hood listing | §6.1.2 / 6.2.1.5 pattern: follow the hood listing and manufacturer instructions | Do not swap in aftermarket mesh “pads” that the listing never evaluated |
Why mesh fails the standalone rule
- Mesh holds grease in the media. Once loaded, it can become a fuel package in the canopy path.
- Secondary code text wants grease filters of rigid construction that will not distort or crush under normal handling (§6.2.3.2–6.2.3.3 pattern), arranged so all exhaust air passes through the filters (§6.2.3.4).
- Baffles drain grease into a drip tray / enclosed metal container (commonly ≤1 gal) instead of storing it in the filter face (§6.2.4 pattern).
- Mesh that sits crooked or compresses leaves bypass gaps — the same failure mode as a warped baffle frame.
Installation checks managers can walk
- Listing mark legible on every removable filter (UL 1046 or the mark your AHJ accepts)
- Filters sit flush; no light gaps at the frame
- Orientation correct — baffles drain into the trough (often marked; secondary text wants ≥45° from horizontal where required)
- Drip tray / trough present and not overflowing into the plenum
- Distance from cooking surface / flue outlet meets the listing or the secondary 18 in / charbroiler 4 ft patterns — do not invent a shorter spacing without listing or AHJ approval
- No standalone mesh pads where the hood listing expects baffles
Dirty or missing filters also cut capture. See smoke not pulling into the hood and nightly staff filter wash vs professional deep clean.
Who it’s for / not for
- For: Managers who inherited mesh pads; multi-unit ops auditing filter stock; anyone rewriting a night-close SOP after a failed inspection
- Not for: Designing a new hood listing; approving a custom mesh+primary assembly without the UL report; treating filter wash as a duct/fan certificate
Sources
- UpCodes — Grease Removal Devices in Hoods (UMC/IMC pattern citing NFPA 96 §6.1.1–6.1.3 mesh rule; §6.2 installation, drip trays, angle)
- UpCodes — Grease Filters, Mesh-Type (mesh not used unless integral to listed hood or listed with primary filter under UL 1046)
- HoodFilters: NFPA 96 filter / listing summary (secondary §6.1.1–6.1.3 and rigid-filter construction notes)
Next step
Pull one filter tonight. If it is mesh with no hood-listing paperwork, or a baffle with no listing mark, bag it and order listed baffles sized to the canopy — do not wait for the next deep-clean night.