Kitchen Exhaust Duct Cleaning San Diego: What Happens Above the Hood

The hood canopy is the part you can see and the part everyone cleans. The duct run and the rooftop fan are where the grease actually collects, and they are where most San Diego kitchens are quietly out of compliance.

Growing up working in restaurants, I never once heard anybody talk about the ductwork. You looked at the hood. If the stainless was shiny and the filters came back clean, the job was done. Nobody climbed a ladder to check the elbow above the ceiling tile, and nobody walked the roof.

That is exactly the blind spot the low bid services rely on. A hood canopy takes forty minutes. A full duct run and a rooftop fan take hours and require access panels, ladders, roof access, and containment. Charge for one and deliver the other and nobody notices, because the customer has no way to see the difference.

This guide walks the whole system from the cook line to the roof. What the duct run actually is, what NFPA 96 requires inside it, why access panels decide whether your kitchen can be cleaned at all, what happens at the rooftop fan, and how to tell in about two minutes whether your last vendor did the work you paid for.

The Three Parts of a Kitchen Exhaust System

Every commercial kitchen exhaust system in San Diego is built the same way, whether it sits over a taco shop flat top in Chula Vista or a hotel banquet line downtown. Three components, connected end to end, all carrying the same grease.

Grease does not stop at the filters. Filters catch the heavy particulate, but vaporized fat passes straight through, cools as it travels, and condenses on whatever metal it touches next. That condensation happens along the entire duct run and it is worst at every point where airflow slows down, which means every elbow, every transition, and every horizontal section.

By the time the air reaches the roof it has dropped most of its grease inside your building. The duct is not a pipe that stays clean because the hood is clean. It is the part of the system with the most surface area, the least visibility, and the highest fire load.

Why the Duct Run Gets Skipped

When a kitchen calls us because their last service felt too cheap, the duct is where we find the answer. There are four reasons it gets left out, and only one of them is honest.

The first is time. Scraping and pressure washing a full duct run is the longest part of the job. A crew that wants three kitchens a night cannot do three full systems a night, so the duct is what gets cut.

The second is access. If the building has no duct access panels, there is no way to reach the interior without cutting new ones. Cutting panels takes skill and adds cost, so a vendor working a tight bid will simply report that the duct was inaccessible, or say nothing at all.

The third is the roof. Roof access requires keys, a ladder or hatch, sometimes property management coordination, and a willingness to work at height in the dark. Plenty of crews simply do not go up.

The fourth is that nobody checks. The hood is the only part of the system the operator ever looks at, so the hood is the only part that has to look right.

What NFPA 96 Requires in the Duct

NFPA 96 is the fire code standard governing commercial kitchen ventilation, and it does not treat the duct as optional. The standard requires that the entire exhaust system, from the hood through the duct to the fan discharge, be cleaned to bare metal at the interval set by your cooking volume and fuel type.

Bare metal is the operative phrase. The standard is not satisfied by reducing buildup or by wiping down what is reachable. If a measurable grease layer remains on the interior duct wall after service, the system has not been cleaned to code, regardless of how good the hood looks from the kitchen.

The standard also requires that any portion of the system that could not be reached be documented in writing on the service report. That requirement exists precisely because inaccessible duct is common, and because a fire marshal reviewing a fire needs to know whether the operator was told. A service report that never mentions an unreachable section is either a report on a fully cleaned system or an incomplete report, and inspectors read it that way.

For a full breakdown of the standard itself, see our guide on what NFPA 96 actually covers. For the documentation side, see our guide to the certificate of compliance.

One more point operators miss. The cleaning interval applies to the system, not to each component separately. You cannot run the hood quarterly and the duct annually to save money. Grease enters the duct on the same schedule it enters the hood, and the code sets one interval for the whole system.

Access Panels and Unreachable Duct

An access panel is a hinged or bolted opening cut into the side of the ductwork so a technician can physically get inside with a scraper, a brush, and a pressure washer. Without them, a duct run is a sealed metal tube with an opening at each end and no way to reach the middle.

NFPA 96 requires access at every change in direction and at regular intervals along horizontal runs. In practice that means a panel at each elbow, a panel where the duct turns from horizontal to vertical, and panels spaced along any long horizontal section above a ceiling.

Plenty of San Diego kitchens do not have them. Older buildings were fitted out before the requirement was enforced consistently, and tenant improvements done on a budget often reuse existing duct without adding access. We see it constantly in converted retail spaces and in strip center units that have cycled through three or four restaurant tenants.

When a kitchen has no access panels, there are two honest paths. Install them, or document in writing that the duct interior could not be reached. The dishonest third path, which is to say nothing and hand over a certificate anyway, is the one that leaves an operator exposed when a claims adjuster starts asking questions.

Installing panels is a one time cost. They are cut, framed, gasketed, and sealed to hold up to the temperatures and the pressure washing, and once they exist your kitchen can be cleaned properly for as long as the building stands. If you are quoting hood cleaning and one bid is dramatically lower, ask both companies whether your duct even has access. The answer usually explains the gap.

The Rooftop Exhaust Fan

The rooftop fan is where the whole system terminates and it is the single most neglected component we find on kitchens switching over to us. When we lift a fan housing on a first clean, the grease underneath is frequently measured in inches rather than in film.

Servicing it properly means tilting or lifting the fan off the curb, cleaning the housing interior, cleaning each blade, cleaning the curb and the top of the duct riser beneath it, and setting the fan back down correctly with the belt tensioned and the bearings checked. A fan set back crooked will vibrate itself into a repair bill, so the reassembly matters as much as the cleaning.

A neglected fan costs you three ways. It loses airflow, which means heat and smoke back up into your kitchen and your line cooks work in a worse environment. It runs harder against the resistance, which shortens motor life. And it becomes the origin point for grease running down onto the roof.

If your kitchen has been serviced for years and nobody ever asked you for roof access, your fan has never been cleaned. That is the fastest diagnostic there is, and operators are usually surprised by how obvious it becomes once they think about it.

Grease Containment and Roof Damage

Grease containment is the absorbent system installed at the base of the rooftop fan to catch what drips out of the housing before it reaches the roof surface. It is a small piece of equipment that prevents a very expensive problem.

Without containment, grease runs from the fan curb onto the roof membrane and spreads. Grease degrades most commercial roofing materials, and the staining alone is enough for a property manager to notice during an annual roof inspection. Once the membrane is compromised, you are looking at roof repair, and most roof warranties are explicitly voided by grease contamination.

That bill lands on the tenant. Nearly every commercial lease in San Diego County makes the restaurant responsible for damage caused by its own equipment, and a grease stained roof is about as clearly attributable as damage gets. We have watched operators get handed five figure repair estimates at lease renewal over a containment system that would have cost a fraction of that.

Containment pads are replaced as part of routine service. If nobody has ever mentioned yours, either you do not have a system installed or nobody has been to your roof, and both are worth finding out about before your landlord does.

How to Tell If Your Duct Was Cleaned

You do not need to climb anything to audit your last service. Pull your most recent service report and run it against these five checks.

There is also a physical check anyone can do. Pull a filter out of the hood and look at the plenum behind it, then look up into the duct opening at the top of the plenum with a flashlight. If you see black buildup starting right where the duct begins, the duct was not touched. Clean duct at that opening looks dull gray and feels dry.

One more signal worth naming. If your kitchen has gotten hotter over the last year, or smoke hangs on the line longer than it used to, that is usually airflow loss from accumulation somewhere above the hood. Operators tend to blame the fan motor. More often it is the duct restricting the air the fan can move.

What a Full System Service Covers

Every job we run at Core is a full system clean. There is no hood only option and no partial scope, because a partial clean does not satisfy NFPA 96 and we are not going to hand you a certificate that says otherwise.

We sheet and protect the cook line and the surrounding surfaces first. We pull and process the filters. We scrape and pressure wash the hood canopy and the plenum. We open every access panel on the duct run, scrape the heavy accumulation by hand, then pressure wash the interior to bare metal through the full run including the elbows and the vertical riser. We go to the roof, lift the fan, clean the housing, the blades, and the curb, service the containment, and set the fan back down with the belt and bearings checked.

Then we document it. Before and after photos of each component including the duct interior and the rooftop fan, an NFPA 96 certificate with full scope broken out, and a fresh sticker for the hood. If we find a section we could not reach, it goes on the report in writing and we tell you what it would take to fix it.

If your ductwork has no access panels, we install them. If your rooftop fan has no hinge kit, we can add one so future service is faster and safer. Those are the two upgrades that convert a kitchen that cannot be properly cleaned into one that can be, permanently.

We service restaurants, bars, breweries, hotels, schools, and institutional kitchens across San Diego County, from Oceanside and Carlsbad down through Mission Valley and Downtown to Chula Vista. Most of our work runs after close so nothing interrupts service. Learn more about our full system hood cleaning, our filter exchange program, and our NFPA 96 inspections.

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