How a Kitchen Hood System Works
The parts of a restaurant exhaust system, how grease moves through them, and what we clean in each one.
The Whole System, Hood to Roof
A kitchen exhaust system is more than the hood you see over the line. It’s 6 parts working together to pull smoke, heat and grease out of the kitchen and up past the roof.
How the air moves
- Cooking sends it up.Heat, smoke and grease vapor rise off the line into the hood.
- The filters catch some.Grease drops out in the baffle filters and runs into the trough.
- The rest keeps going.What gets past the filters coats the plenum and the duct.
- The fan pushes it out.The rooftop fan pulls the air up and blows it out above the roof.
- Containment catches the drips.Grease the fan throws off drains into a collector, not onto the roof.
Each Part, and What We Clean
The numbers match the drawing above. We clean all 6 on every hood cleaning.
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Hood Canopy
The stainless canopy over the cooking line. It catches the heat, smoke and grease vapor coming off the line, and grease condenses on its inside walls.
What we clean: inside and outside surfaces, scraped and degreased down to bare metal.
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Filters & Grease Trough
Baffle filters make the air turn sharp corners, so heavy grease drops out and runs into the trough below. They catch a lot of grease, but not all of it.
What we clean: every filter degreased and washed on site, and the trough emptied and cleaned. More on filter cleaning
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Plenum & Duct Collar
The hidden space behind the filters, where the hood connects to the duct. Everything that gets past the filters passes through here, so grease builds up fast and out of sight.
What we clean: the plenum walls and the duct collar, every time.
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Ductwork
The duct carries the exhaust from the hood to the roof, sometimes up through several floors. Grease coats the inside, and a fire in the duct is the hardest kind to reach. Bolted access panels let us get inside.
What we clean: every accessible foot of duct, through the access panels.
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Rooftop Exhaust Fan
The fan on the roof pulls the air up the duct and blows it out. Its wheel spins in the grease-laden air, and buildup can throw it off balance and slow it down. Most fans hinge open so the wheel can be reached.
What we clean: the wheel from underneath, inside and above, plus the housing and curb. If the fan or motor is worn out, we replace it.
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Grease Containment
A collector at the fan’s grease drain. It catches what the fan throws off, so grease stays off the roof, where it breaks down the membrane and can feed a rooftop fire.
What we clean: the containment around the fan, serviced at every cleaning.
Why Cleaning Only the Hood Isn’t Enough
The hood is the part you can see, so it’s the part that gets wiped down. But the grease that reaches the plenum, duct and fan is the grease that feeds a duct fire, and it’s the part a fire inspector asks about.
NFPA 96 calls for cleaning the whole system, on a schedule set by what and how much you cook. That’s why every A-1 hood cleaning covers all 6 parts, and why you get before and after photos of the duct and fan, not just the hood.
- All 6 parts cleaned on every visit
- Before and after photos of the hood, ducts and fan
- A dated service sticker on the hood
- Scheduled after close, 24/7
Schedule Your Hood Cleaning
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