The Hood Is the Starting Point, Not the Whole Job
Kitchen ventilation cleaning is one of those services where the visible part of the job — the hood — accounts for a fraction of where grease actually accumulates. Most of the cleaning effort in a proper service goes into the parts you can't see: the interior of the duct, the fan housing, and the discharge point at the roof. That's where grease builds to hazardous levels.
A cook line generates grease-laden vapor all day. The ventilation system is designed to capture that vapor and exhaust it out of the building. As it travels through the duct, grease condenses on the walls. Horizontal sections and elbows accumulate the most, because that's where airflow slows and grease has time to settle and adhere.
What Each Component Requires
Hood filters are the first line of capture and the most frequently serviced component — in a busy kitchen, they need attention weekly or biweekly. Professional cleaning covers the filters, the filter housing, and the grease collection cup or channel behind the filters.
The hood plenum — the interior chamber — catches vapor that makes it past the filters. It gets scraped and degreased as part of a full service. Above the plenum, the duct run carries the exhaust to the roof. Accessing the duct requires opening or cutting access panels, and a thorough cleaning works through the entire duct run, not just the sections immediately above the hood.
At the top of the system, the exhaust fan pulls everything up and out. The fan housing, fan blades, and the grease collection point at the fan base are cleaned. The fan is the heat source in the system, and grease on or near the motor is the most direct fire risk in the whole assembly.
Cleaning Frequency
NFPA 96 sets minimum cleaning intervals based on cooking volume. The practical answer for most full-service restaurants is quarterly to semi-annual. If you're doing high-volume frying or charbroiling, quarterly is the appropriate starting point. The right contractor will document the condition of your system after each cleaning and advise on whether the interval is appropriate for what they found.
What You Get at the End
Written documentation with before-and-after photos and a record of what was cleaned. Any areas with restricted access noted. Condition of the system described. That's your compliance record and your starting point for the next service interval.