Kitchen Exhaust Not Cleaned for Years: What to Expect From the First Clean

Pictured above: the inside of a kitchen exhaust duct at one of BC Air’s cleaning and maintenance projects in Chai Chee, with a film of grease on the walls and ceiling of the section and liquid grease lying along its floor. It is reused here because it is what “the duct” looks like from the inside, and it is the part of the system that no one in the kitchen ever sees.

You have taken over a unit, or the contractor has changed, or you have just realised that nobody can say when the exhaust was last cleaned. The honest answer might be “years”. The question that follows is what the first clean will be like, because it will not be like the ones on a schedule. It will take longer, it may be done in more than one step, and it is the visit most likely to find something.

This post is about that first clean: what is different, what to settle before the crew arrives, and what you should have in your hands afterwards. It gives no prices. What it costs depends on the system and what is found, and we quote after an inspection.

Why the first clean is a different job

Grease does not just pile up in a kitchen exhaust, it bakes. Each cooking session hardens the layer underneath. What starts as a soft, wipeable film turns, over months, into a hard, lacquer-like coating bonded to the metal. In a neglected system the deposit can be several millimetres thick, and in the worst ones centimetres. The same system on a regular schedule never gets that far, because the film is removed while it is still soft.

That is why a system with a long gap behind it cannot be treated as a normal clean with a bit more effort. A degreaser sprayed over a thick baked deposit does not get through it. It can leave a surface that looks clean while a hard layer is still sitting underneath. The right first step is to remove the bulk, and only then to bring in the chemistry. We explain the two methods and why a badly loaded system needs both in chemical degreasing versus manual scraping.

What to ask before you book it

A fair quote for a backlogged system is not a number given over the phone. Here is what to ask, and what a straight answer sounds like.

• “Will you inspect it first?” The answer should be yes. We inspect the hood, the ducting and the fan, and look at your actual cooking volume and hours, before we recommend anything. A heavily soiled system can need a longer window than a normal clean, and we confirm the timing after we have seen it. Our site survey post lists what to send so the first conversation is useful.
• “Is this one night, or is a second visit likely?” Nobody can promise this without looking, but a contractor should be able to say what would decide it. On one kitchen we serviced, a high-volume noodle operation that had missed several cleaning cycles, the grease layer in the ductwork was so thick that scraping alone took most of the first visit. The chemical treatment on the follow-up visit is what showed the pitting and surface corrosion underneath.
• “What exactly is covered?” The whole system, not a wipe-down of the visible stainless: hood inside and out, filters, the accessible duct interior, the fan, and the make-up air grilles. Check the scope against our 10-point servicing checklist. If the duct is not opened, it is not cleaned.
• “What happens if you find a fault?” A first clean opens parts that have not been opened in years, so it finds things. Settle in advance who can approve extra work on the night. We cover that decision in a fault found during an exhaust clean.

The order of work in a system with a backlog

The sequence that gives the best result on a heavily soiled system is the same one every time, and it is worth knowing so you can tell whether it is being followed:

• Bulk removal first. Heavy deposits are scraped out so the degreaser can reach the surface. A crew that sprays first is making work for itself and for you.
• Then the chemistry, with time to work. The degreaser needs dwell time. One that is wiped off straight away has done almost nothing. On heavy deposits that means a stronger mix and a longer contact time before it is agitated and flushed.
• Flush and inspect. The surface is rinsed and checked under a torch, down to bare or near-bare metal.
• Work from the hood down to the fan. That way nothing is pushed back into a section that has already been cleaned.
• Filters come out. Baffle filters are removed and cleaned, never cleaned in place, and replaced when worn.

Older systems also have thin or corroded panels that have to be handled with care. If the crew treats the duct like a pipe to be hosed, ask them to slow down.

What the first clean can show that no earlier clean did

Three things tend to come to light, and none of them is the cleaner’s fault.

• What the grease was hiding. Metal that has been under a hard layer for years can show pitting or surface corrosion once it is clean. The report should say where and how bad, with a photograph.
• Faults in the fan and motor. A fan loaded with grease is out of balance, and that wears the bearings. Once it is opened and cleaned, bearings, belts, vibration and the motor connections can be checked properly. Because we stock motors, fans, fan parts and control components in-house, many faults can be repaired or replaced on the spot, though some need a proper look and a plan first.
• Sections that could not be opened. If a stretch of duct has no access door, or the door is sealed behind a ceiling with no panel, it cannot be cleaned, and the report should say so in plain words. That line matters more than any other on it. We set out why in the duct you cannot open is the duct that never gets cleaned.

One more item belongs on the same visit. The grease we remove also fouls the fire suppression nozzles and coats the fusible links over the cooking line, and a greased-over link may not release at the temperature it was rated for. We can service the suppression system on the same visit as the clean, so one team sees the whole cooking line. See fire suppression maintenance. Nobody should be moving or covering a nozzle to make the cleaning easier.

Keep the “before” photographs

On a first clean the before-and-after photographs are worth more than on any later one. They are dated proof of the condition you inherited and of what was done about it. Every clean here comes with before-and-after photographs and a service record you can show NEA, SCDF, your landlord or your auditor. If you took over the unit recently, those photographs and the record are what separate “it was like that when we arrived” from “nobody checked”. Our post on taking over an F&B unit covers what to look at before you sign.

Ask for the report to name anything that was not cleaned and why. A section named on this report that is still named on the next one is a section that has been accumulating through two cleans.

The morning after

The kitchen should not be cooking on a system that has only been cleaned, it should be cooking on one that has been checked. Before the first burner is lit, run the opening check from kitchen exhaust cleaning night: filters seated and the right way round, the fan running without a new noise or vibration, and the hood actually pulling smoke and heat. If a motor, fan or drive was changed, confirm the airflow before service.

Then set the interval, so it never gets here again

The first clean fixes the backlog. What keeps it fixed is the interval. Published guidance is that most commercial kitchens need the whole system cleaned every one to three months, with heavy wok, grill and deep-frying kitchens often monthly and lighter kitchens quarterly. NFPA-96 is the framework the industry works to, and both NEA and SCDF expect the system to be kept clean, safe and documented. We do not apply a fixed rule: after the first clean we know what your kitchen produces, and we recommend an interval from that. A maintenance program puts it on a schedule with a record after each visit. The reasoning is in how often a kitchen exhaust must be cleaned.

WhatsApp BC Air on 8989 2833 with the location, what you cook and for how many hours, the last clean if you know it, whether the duct has access doors, and what you are seeing. A photo of the hood interior or an opened access panel helps. We are on 24/7 standby, and scope and pricing follow an inspection. Our kitchen exhaust cleaning covers the hood, the filters, the accessible duct and the fan.

The short version

• Grease bakes. A system with years of neglect behind it is a heavier job than a normal clean.
• Ask for an inspection first, and ask what would make it one night or two.
• The right order is bulk removal, then chemistry with dwell time, then flush and inspect, then document.
• Expect the first clean to find things: corrosion under the grease, fan and motor faults, and sections that cannot be opened.
• Keep the before photographs and the report. Anything not cleaned should be named on it.
• Set the interval afterwards so the backlog does not come back.

Related reading: signs your hood is overdue for a deep clean · reopening after a long closure · how often a kitchen exhaust must be cleaned