Phoenix Journal · Extraction
A well-designed kitchen extract system moves a great deal of air, and air in a hurry makes noise. Getting the acoustics right protects your staff, keeps neighbours onside and stops a planning condition turning into an enforcement notice.
Acoustic design
A commercial kitchen extract system shifts a large volume of air at speed, and moving air is never silent - the question is only how much of that noise reaches your team on the line and your neighbours over the fence.
Noise rarely gets designed in from the start. A canopy is sized for the cooking suite, a fan is chosen to hit the airflow, and the acoustic consequences turn up later as a headache on the pass or a complaint through the letterbox. Treating sound as an afterthought is expensive, because the fixes - bigger attenuators, anti-vibration mounts, a slower fan on a larger duct - are far cheaper to specify on paper than to retrofit into a live building. This piece walks through where the noise comes from, the UK rules and targets that shape what "acceptable" means, and the practical measures that keep a system both quiet and compliant.
It helps to separate the two problems, because they have different owners and different fixes. The first is noise inside the kitchen, which is a health and safety matter for your staff. The second is noise breaking out of the building - through the discharge point, the plant enclosure or the fabric of the duct - which is an environmental and planning matter for the people around you.
Most of the sound energy starts at the fan. A centrifugal or mixed-flow unit generates a broadband roar plus tonal components tied to its blade-passing frequency, and that tone is often what makes a system feel intrusive even when the overall level looks modest. On top of that you get regenerated noise wherever air is forced to change direction or squeeze through a tight fitting - sharp bends, a badly transitioned canopy plenum, dampers left half closed, or a duct sized too small for the design flow. As a rough rule, doubling the air velocity in a duct raises the regenerated noise by around 15 decibels, so an undersized run is punished heavily. Finally there is structure-borne noise and vibration: a fan bolted hard to a roof deck or a mezzanine will pump low-frequency energy straight into the building, where it re-radiates from ceilings and walls as a hum that no amount of in-duct silencing will touch.
Grease is the quiet complicating factor. Acoustic linings and attenuator splitters sit in a duct that is, by definition, carrying grease-laden vapour, so any acoustic material has to be cleanable, non-shedding and compatible with a system that will be jet-washed on a schedule. That constraint rules out the soft, fibrous absorbers you might use in an office supply duct and pushes you towards purpose-made kitchen-rated silencers.
The thresholds
There is no single legal noise limit for a kitchen extract fan, so design is governed by a cluster of standards and duties rather than one figure. Inside the kitchen, the Control of Noise at Work Regulations 2005 set the benchmarks for staff exposure. Outside, most local authorities assess plant noise against the method in BS 4142:2014+A1:2019, which compares the rating level of your system with the background sound level at the nearest neighbour. For acoustic comfort in the spaces you serve - a dining room, say - designers lean on BS 8233 and Noise Rating (NR) curves. Keep these three anchors in view and the target level for any given project becomes something you can actually calculate.
Read together, these set the envelope. You want the fan and its regenerated noise held well below the point where kitchen staff need hearing protection, the break-out level at the boundary sitting at or below the measured background so a BS 4142 assessment does not flag adverse impact, and the airborne path into any adjoining dining or sleeping space attenuated enough to meet a sensible NR or dB target. Where a kitchen sits under residential floors, that last figure drives the whole design, because night-time background levels are low and even a modest tonal hum can push you into complaint territory.
Good acoustic performance is mostly the sum of unglamorous decisions made early. The single most effective move is to size the ductwork generously and pick a fan that delivers the required volume at a lower speed, because a slower fan on a fatter duct is quieter at source and generates less noise along the way. Everything after that is about catching what is left.
One coordination point is easy to miss. Attenuators and silencers occupy real space in the duct run, and that run also has to pass through fire-rated walls and floors with the right dampers and sealing. Squeeze the two requirements together late and something gives - which is why the acoustic layout and the fire strategy need to be reconciled on the same drawing, a theme we pick up in the link between ventilation and fire compartmentation.
Acoustic performance also degrades quietly over time. A grease-clogged attenuator loses absorption, a corroded anti-vibration mount goes solid, and a fan running against a fouled, high-resistance system speeds up and grows louder to hold its airflow. A clean, well-maintained extract system is a quieter one, and the routine deep clean that keeps you compliant with fire and hygiene duties is the same visit that protects the acoustic design you paid for.
Questions
There is no single national limit that applies to every fan. Inside the kitchen, staff exposure is governed by the Control of Noise at Work Regulations 2005, which set a lower action value of 80 dB(A) and an upper value of 85 dB(A). Outside, most local authorities assess plant noise using BS 4142:2014, comparing your system against the background level at the nearest neighbour, and a planning condition may fix a specific limit for your site.
BS 4142:2014 compares the rating level of your ventilation plant with the measured background sound level at the affected property. The rating level includes a correction for tonal or intermittent character, which is why a whining fan can fail even when it is not especially loud overall. A rating level around 5 dB above background is taken as an indication of adverse impact, and around 10 dB above as significant adverse impact.
No. A kitchen extract duct carries grease-laden vapour and is cleaned regularly, so ordinary fibrous acoustic linings are unsuitable - they shed, absorb grease and become a fire and hygiene risk. You need purpose-made, grease-rated attenuators with cleanable, non-shedding splitters that can be inspected and washed as part of your normal maintenance regime.
Yes, more than people expect. As grease builds up in the duct and across the fan, the system resistance rises and the fan has to work harder and faster to hold its airflow, which increases noise. A fouled attenuator also loses its sound absorption. Keeping the ductwork clean protects both the airflow and the acoustic performance you designed for, alongside the fire and hygiene benefits.
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.