Grease leaves the filters as vapor and condenses along the plenum, the horizontal duct runs and the riser before it ever reaches the fan on the roof, so by the time a system is heavily loaded most of it sits where nobody can see it from the kitchen floor. We clean all of it: filters pulled, canopy and plenum washed to bare metal, access panels opened to reach the duct and riser, and the rooftop fan taken apart to clean housing, blades and curb.
El Paso splits the oversight, and that catches operators out. The Department of Public Health inspects your kitchen and publishes the score, and on ventilation its interest stops at grease and condensation on walls and ceilings. The inside of your ductwork belongs to the Fire Marshal, under the 2021 International Fire Code the city adopted as Chapter 9.52 of its code, where commercial kitchen exhaust hoods sit in Section 606. A kitchen can post a strong score and still be carrying a load that fails on the fire side.
Worth being precise about the standard, because most vendors are not: the city ordinance enforces the fire code and does not name NFPA 96 anywhere. NFPA 96 is the standard the trade cleans to and the one your insurer and your fire inspector will recognize, so it is what we clean and document against.
How often you need service comes down to what you cook, and comal, mesquite and fryer-heavy lines load a system faster than a national default assumes. Solid fuel needs the most frequent attention, then high-volume, charbroil and wok, then moderate-volume kitchens, then low-volume operations. We set your interval from the grease load we measure, and if any part of the system cannot be reached, you get that in writing.
