Phoenix Journal · Extraction
A commercial extraction fan does not get louder for no reason - the extra noise is nearly always grease restricting airflow or a fan wearing out. Here is how to read the sound and put it right.
Kitchen extraction
A rising note from your canopy is not just an annoyance across a busy service - it is your extraction system telling you something has changed, and usually not for the better.
When a commercial kitchen extract system is running well, it settles into a steady background hum that your team stops noticing within minutes of the first order. So when the sound climbs - a new drone, a rattle, a whine that carries over the pass - the change itself is the signal. Fans do not simply decide to get loud. The extra noise is energy being spent on something other than moving air cleanly out of your kitchen.
Broadly, a louder extraction system points to one of two things. Either the air is fighting its way through a system that has silted up with grease, or the fan and its drive components are wearing, loosening or falling out of balance. Often it is a bit of both, because a system carrying heavy grease deposits makes the mechanical parts work harder and age faster. Understanding which cause is in play matters, because the fix - and the risk of ignoring it - is very different for each.
It helps to think about what your extraction is meant to do. It draws heat, steam, smoke and airborne grease off the cooking line, carries it through a canopy and filters, along a run of ductwork and out through a fan to the outside air. Every one of those stages can add resistance. As resistance builds, the fan has to work against it, and a motor working harder is a motor making more noise. So the volume is, in a real sense, a rough gauge of how freely your system is breathing.
In the majority of cases we attend, yes - grease is the quiet culprit behind a noisier fan. Every hour your kitchen cooks, a fine aerosol of oil and fat is drawn up into the canopy and carried through the system. Some is caught by the filters, but the rest coats the inside of the ductwork and, eventually, the fan itself. It builds slowly and invisibly, which is exactly why the first thing most operators notice is not the grease - it is the sound.
Grease narrows the airway. A duct with a heavy internal coating has a smaller usable bore, so the fan has to pull harder to shift the same volume of air. That extra effort shows up as a deeper, more strained note and, often, as reduced draw at the canopy - steam lingering over the pans, or heat backing up into the kitchen. If the fan sits at the end of a warm summer run of long, hot services, the strain is worse still, which is part of the wider operational case for keeping extraction clean through summer.
There is a second, more mechanical way grease raises the volume. Deposits do not settle evenly on a spinning impeller. A film that is thicker on one side shifts the fan's centre of gravity, and an out-of-balance impeller vibrates. That vibration is both a new noise source and an accelerant for bearing wear. So grease that starts as an airflow problem can quietly become a hardware problem.
In the UK, how clean is clean enough is not a matter of opinion. The recognised benchmark is TR19 Grease, the standard published by the Building Engineering Services Association (BESA) and referenced by the Association of British Insurers. It sets measurable thresholds: mean grease deposits across the system should sit below 200 microns, any single reading above 500 microns calls for immediate localised cleaning, and verified surfaces should be brought below 50 microns after the work. Deposits are checked using recognised methods such as the wet film thickness test for soft grease and the deposit thickness test for harder, carbonised build-up. A system cleaned and verified to that standard is a system that breathes freely - and runs quietly.
There is a compliance edge to this too. Grease that is left to accumulate is a genuine fire risk in the ductwork, and most commercial buildings and contents insurance policies expect you to prove your extraction has been cleaned on a TR19 Grease schedule. A louder fan is worth acting on for the noise alone, but the paperwork behind it is just as good a reason.
If your extraction has been cleaned recently and the noise has still crept up, the fan unit itself is the next place to look. Extract fans are simple machines that live a hard life - they run for the whole of every service, in warm, greasy air, often on a roof exposed to the weather. Components wear, and each type of wear tends to have its own signature sound.
Bearings are the most common mechanical cause of a louder fan. They support the spinning shaft, and as they wear they begin to grind or rumble rather than turn smoothly. A dry, worn bearing produces a low growl that gets worse over weeks, and it should never be ignored - a failed bearing can seize a fan completely and leave a kitchen with no extraction at all, mid-service.
Drive belts, on belt-driven fans, are another frequent offender. A belt that has stretched and gone slack will slip and squeal, particularly on start-up. One that has been over-tightened puts extra load on the bearings and adds its own strain to the sound. Belts and pulleys also pick up grease and dust, which makes them run rough. Where a fan uses more than one belt, they should be replaced as a matched set so the load stays even.
Balance and alignment tie the whole picture together. An impeller thrown off balance - by uneven grease, by a bit of debris, or by minor damage - vibrates, and that vibration travels through the bearings, the mounts and the surrounding ductwork as a rattle or a hum. Misaligned pulleys do the same. Because vibration wears the very parts that keep the fan quiet, a small imbalance left alone tends to snowball into a bigger, more expensive repair.
You can often narrow it down before anyone lifts an inspection hatch. A steady deepening drone with weaker draw usually means grease and restricted airflow. A grinding or rumbling that rises over time points to bearings. A squeal, especially on start-up, suggests a belt. A rattle or shudder that you can feel as much as hear points to imbalance or loose mounts. None of these are jobs to guess at from the floor, but the sound gives an engineer a very good head start.
The worst thing you can do with a louder extraction fan is turn the radio up and carry on. Noise is the cheapest warning your system will ever give you, and it almost always gets more expensive the longer it is left. A grease-choked duct is a fire risk and an insurance problem. A worn bearing is a fan failure waiting for your busiest night. Neither improves on its own.
Start by getting the system properly inspected and cleaned to TR19 Grease. In a large share of cases that alone resolves the noise, because it removes the airflow restriction and rebalances the impeller in one visit. It also gives you the documented proof of cleaning your insurer expects. If the fan is still loud once the system is clean and breathing freely, you have isolated a mechanical fault - and a clean fan is far easier and safer for an engineer to inspect, lubricate or repair.
Beyond the immediate fix, the real answer is a planned schedule. Extraction that is cleaned on a frequency matched to how hard your kitchen cooks rarely gets the chance to grow loud in the first place, and a fan that is checked as part of that visit gets its worn belts and tired bearings caught early. A quieter kitchen is usually a cleaner, cheaper, safer one - the same neglect that raises the volume also drives up your running costs, which is the direct link between dirty extraction and higher energy bills.
If your extraction has found a new voice, treat it as a prompt rather than a nuisance. Have it looked at, cleaned to standard, and put on a schedule - and the hum should fade back into the background where it belongs.
Questions
It can be both, which is why it is worth acting on. The most common cause - grease build-up in the ductwork - is a recognised fire risk and can invalidate your insurance if it is left uncleaned. A mechanical cause such as a worn bearing can lead to the fan seizing completely, leaving your kitchen with no extraction mid-service. The noise itself is harmless, but what it signals rarely is.
In most cases, yes. A large share of louder fans are caused by grease narrowing the airway and unbalancing the impeller, so a thorough clean to the TR19 Grease standard removes the restriction and lets the fan spin freely and evenly again. If the fan is still loud once the system is verified clean, you have isolated a genuine mechanical fault - and a clean fan is far safer and easier for an engineer to inspect and repair.
Phoenix Duct Clean · by the numbers
The right kit only helps if the system stays clean. Phoenix degreases canopies, filters and ductwork to TR19 Grease - UK-wide, overnight.