Cooking Fires Start Where Grease Collects
The U.S. Fire Administration names cooking as the leading cause of home fires. In 2021, residential building cooking fires numbered about 170,000 and caused 135 deaths and 3,000 injuries, and unattended cooking equipment was a factor in 37 percent. A clean hood doesn't replace watching the stove, but grease in filters and ducts gives a pan fire more to reach.
Degreasing Metal Hood Filters at the Sink
Turn Off the Hood and Let It Cool
Filters come out through clips or a slide.
Soak in Hot, Soapy Water
Use a degreasing dish soap and let the filters sit.
Scrub Gently
A soft brush works the grease out of the mesh or baffles.
Rinse and Dry Completely
Reinstall only when dry.
Wipe the Hood Interior
Clean the grease film above the filters while they're out.
Check your hood's manual first; some metal filters are dishwasher-safe. Charcoal filters in ductless, recirculating hoods get replaced, not washed.
Where a Kitchen Hood Duct Must Go
| Rule | Section |
|---|---|
| Vents outdoors, never into an attic or crawl space | M1503.3 |
| Smooth-interior, airtight duct with a backdraft damper | M1503.3 |
| Independent of other exhaust systems | M1503.3 |
| Listed ductless hoods are an exception | M1503.3 |
| Makeup air for hoods rated above 400 cfm | M1503.6 |
A hood that vents into the attic leaves grease on insulation and framing; the attic ductwork page covers the other exhausts with the same rule.
When the Duct Needs a Professional
- Grease drips from the hood or collects around the fan
- The hood is loud but moves little air, even with clean filters
- The outdoor damper sticks with grease
- You're unsure whether the hood vents outdoors at all
A technician degreases the fan and duct, checks the damper and termination, and confirms where the duct actually ends.
Airflow Minimums and Makeup Air
Section M1505.4.4 sets the minimum kitchen exhaust rate at 100 cfm for a fan run intermittently, or 25 cfm for continuous operation. Large hoods pull the other way: above 400 cfm, the code requires makeup air to replace what the hood removes. The full set of household exhaust rates is on the whole-home ventilation page.