Guide
Hood filters: clean vs replace decision
Baffle filters are designed to be cleaned and reused. They are not disposable like a coffee filter. The decision is not “how old is this filter by calendar,” it is “does this filter still seal, stay rigid, and pass air only through the baffles?” Damaged filters dump grease into the plenum and duct between professional cleans. Staff filter wash is not a substitute for a full-system clean to bare metal.
Short answer
Clean on a volume-driven cadence (often daily to weekly in busy kitchens). Replace when you see warping, corrosion, dents, holes, loose rivets, missing baffles, or a frame that no longer sits flush — secondary manufacturer and service guides treat those as replace-now conditions, not “one more scrub.” There is no fixed NFPA calendar for filter life; lifespan commonly ranges from months to a couple of years depending on volume, humidity, and cleaner chemistry. Mesh filters are not allowed as standalone grease removal devices under NFPA 96 secondary summaries (UL 1046 listing exceptions only). Your AHJ’s adopted edition wins.
Clean vs replace table
| Condition | Action | Why it matters |
|---|---|---|
| Greasy but flat, intact baffles, flush fit | Clean — soak, scrub, dry, reinstall | Baffles are reusable; grease load is what you manage between professional visits |
| Warped / bent frame; won’t sit flat | Replace | Gaps let grease bypass into plenum/duct (NFPA 96 secondary: all exhaust air must pass through filters) |
| Corrosion, holes, dents, missing baffle sections | Replace | Rigid construction that won’t crush or distort is a listed-filter requirement in secondary NFPA 96 summaries |
| Rivets loose or falling out | Replace (or repair only if you can restore rigid listing-compliant condition) | Manufacturer handbook flags riveted filters for rivet fatigue under frequent handling |
| Polymerized / varnish grease that survives a full soak | Try professional filter exchange / industrial degrease once; if still saturated or distorted, replace | Secondary ops guides note diminishing returns on in-house scrubbing |
| Standalone mesh / wire filters | Replace with listed baffles (unless integral to a listed hood per UL 1046 exception) | NFPA 96 §6.1.3 secondary: mesh not used as standalone grease removal |
| No legible listing mark (UL / equivalent) | Replace with listed filters | Secondary handbook: listed grease filters per UL 1046 / CAN-ULC S649 hooks |
| Solid-fuel line without spark arrestor path | Confirm spark-arrestor / approved arrangement before “just washing baffles” | NFPA 96 Ch. 15 secondary summaries require spark control ahead of grease removal |
What “clean” means (staff job)
- Cool the line and shut the exhaust fan before pulling filters
- Baffles vertical when reinstalled so grease drains into the trough, not sideways into gaps
- Hot water + metal-safe degreaser; avoid bleach / harsh alkalis that accelerate corrosion (manufacturer handbook)
- Hand wash, commercial dishwasher (if manufacturer allows for that material), or overnight soak tank — then dry fully before reinstall
- Wipe the drip tray / grease trough under the filters every cycle — a clean filter over a full trough still drips fuel
- Inspect for damage every wash; set damaged units aside instead of forcing them back in
Keep cleaning
- Listed baffle filters that seat flush with no light gaps
- Channels clear after soak; no soft / crushed frame
- Matching set so the bank fills the opening without improvised cardboard spacers
- Written staff cadence that matches your volume (fryer/char lines wash more often)
Replace now
- Light showing between filters or at the hood track
- Filters that “float” or get sucked up into the hood (air balance + fit problem; don’t paper-tape them)
- Aluminum or soft frames crushed from dishwasher abuse or drops
- Assuming a filter wash sticker equals a duct/fan clean
Field decision checklist
- Seat test — reinstall dry; look for gaps along the track and between neighbors
- Rigid test — press gently on the frame; permanent bend or crush = replace
- Listing — find the UL / listing stamp; no stamp, treat as non-compliant stock
- Material match — don’t mix lightweight aluminum into a bank that was stainless if the fan already pulls them off-track
- Solid fuel — confirm spark-arrestor arrangement before ordering plain baffles (Chapter 15 secondary rules on solid-fuel monthly reality check)
- Scope split — staff owns filters + trough; certified cleaner owns plenum, duct, fan, rooftop cup
Who it’s for / not for
- For: kitchen managers setting wash cadence, facilities leads deciding whether to order a new bank, anyone who just failed an inspection over gaps or mesh
- Not for: quoting filter prices (regional Unknown), designing a hood, or claiming staff wash satisfies the full NFPA 96 exhaust clean
Sources
- HoodFilters — Hood Filter Handbook (PDF) (manufacturer; NFPA 96 §6.1.1–6.1.3 / §6.2.3 listing & mesh notes; clean methods; replace on dents/corrosion/holes/warp; no fixed calendar life)
- HoodFilters — NFPA 96 filter & grease-removal excerpts (secondary; listed filters, mesh ban, rigid construction, solid-fuel spark arrestor hooks)
- Gateway Cleaning — how to clean commercial hood filters (secondary; clean steps; replace on warp/corrosion/gaps; staff filter wash ≠ full-system compliance)
- BOH — restaurant hood filter cleaning guide (secondary; baffle reuse model; polymerized grease / exchange framing)
- Superior Clean — NFPA 96 scope notes (secondary; filters + grease cup as part of full path; canopy-only mistake)
Next step
Pull one bank tonight after close. Wash what seats flush. Bag anything warped, holed, or gap-prone and order listed replacements before the next fire walk — don’t reinstall a filter that leaks light.