Duct cleaning & ventilation hygiene
Two identical kitchens, two identical systems, yet one needs cleaning twice as often. The difference is rarely the cooking. A system that moves air poorly fouls faster, and shortens every cleaning interval.
Two identical kitchens, two identical extract systems, and yet one needs cleaning twice as often as the other. The difference is rarely the cooking alone. More often it is the airflow: a system that moves air poorly fouls faster, and a system that fouls faster has to be cleaned more often. Poor ventilation does not just fail to clear the air; it quietly shortens the interval between every clean.
It is tempting to treat cleaning frequency as a fixed property of a kitchen, set by how much it cooks. In reality the condition and performance of the ventilation system itself is a major driver. When air moves through ductwork at the right velocity, much of the grease and dust it carries stays entrained and is driven out of the building. When the airflow is weak or uneven, more of that material drops out and settles on the duct walls along the way. The same effluent, moving through a worse-performing system, leaves more behind, and the deposits it leaves become the seed for the next layer.
Why slow air fouls faster
The physics is well understood in ventilation engineering: as the velocity of air in an extract duct falls, the rate at which grease and particulates deposit on the internal surfaces rises. Air moving briskly keeps particles suspended and carries them to discharge; air moving sluggishly lets them settle. So anything that lowers duct velocity, an undersized or throttled system, blocked filters, a fan that is no longer pulling as it should, tips the balance towards deposition. The kitchen may be producing exactly the same amount of grease, but a larger share of it is now sticking inside the ductwork instead of leaving the building.
Worse, the process compounds. A grease-coated surface is stickier than clean metal, so it captures passing particles more readily than a clean duct would, and each layer of deposit makes the next layer form faster. Narrowing the duct with build-up also raises resistance and drops the airflow further, which increases deposition again. A neglected system does not foul at a steady rate; it foul at an accelerating one, because every deposit makes the conditions for the next deposit worse. That is why a system left too long between cleans can seem to deteriorate suddenly, when in fact it has been compounding quietly all along.
The fan is a common culprit in this spiral. As grease and dust build up on fan blades and in the housing, the fan moves less air, which reduces both the capture at the canopy and the velocity in the duct. Less capture means more grease escapes into the room and the near ductwork; lower velocity means more of what does enter the duct settles out. A dirty fan therefore attacks the problem from both ends at once, and a system with a neglected fan will foul markedly faster than the same system with a clean, properly performing one.
What makes it worse
Beyond velocity, the thermal condition of the ductwork plays a part. Where extract ducts run through cold spaces or are poorly insulated, the warm, moisture-laden air from the kitchen can condense on the duct walls, and that film of moisture makes grease deposits stickier and harder to shift. Long horizontal runs, sharp bends and cold external sections all become preferential fouling points for the same reason. All of this means the cleaning interval is not really a fixed number to be looked up; it is an outcome of how well the whole system is designed, performing and maintained, and it is tied directly to running cost, since a fouled, high-resistance system also wastes energy, which is part of the wider work of cutting ventilation running costs.
Breaking the cycle
The encouraging flip side is that a well-performing system partly protects itself. Keep the airflow strong and even, the fan clean, the filters maintained and the ductwork clear, and more of the grease is carried out of the building rather than deposited inside it, which slows the rate of fouling and lengthens the safe interval between deep cleans. Neglect any of those and the system tips into the compounding spiral, cleaning becomes needed sooner, and the cost climbs. This is the operational heart of why a well-maintained extract system is cheaper to run over time, the same logic behind the operational case for cleaner extraction in summer. Look after the airflow, and the cleaning frequency looks after itself.
Questions
Yes. Cleaning frequency is not fixed by cooking volume alone; the performance of the system is a major driver. A system that moves air poorly lets more grease and dust settle inside the ductwork, so it fouls faster and needs cleaning more often than a well-performing one handling the same load.
Because as duct velocity falls, the rate at which grease and particulates deposit on internal surfaces rises. Fast-moving air keeps particles suspended and carries them to discharge; slow air lets them settle. Anything that lowers velocity tips the balance towards deposition inside the duct.
A grease-coated surface is stickier than clean metal, so it captures passing particles more readily, and each layer of deposit makes the next form faster. Build-up also narrows the duct and lowers airflow further. So a neglected system fouls at an accelerating rate, not a steady one.
As grease and dust build up on the fan, it moves less air. That reduces capture at the canopy, so more grease escapes into the room and near ductwork, and lowers duct velocity, so more of what enters settles out. A dirty fan speeds up fouling from both ends at once.
Keep the airflow strong and even, the fan clean, the filters maintained and the ductwork clear. More grease is then carried out of the building rather than deposited inside it, which slows fouling and lengthens the safe interval between deep cleans.
Phoenix Duct Clean · by the numbers
Poor airflow may be fouling your ductwork faster than it needs to. Talk to Phoenix about restoring performance and setting a cleaning schedule based on evidence.