Phoenix Journal · Extraction
If your kitchen feels like a sauna by mid-service, it is almost never the weather - it is heat that has nowhere to go. Here is why it happens and how to fix it.
Kitchen comfort & airflow
If your kitchen feels like a sauna by mid-service, it is almost never the weather doing it - it is heat that has nowhere to go.
Commercial kitchens run hot by nature. Fryers, ranges, chargrills, combi ovens and pass-through dishwashers pour energy into a small, enclosed space, and unless that heat is captured and removed as fast as it is produced, the room simply climbs. A busy line can push wet-bulb conditions well past anything you would tolerate in an office, and the discomfort is not just morale - it slows service, raises the risk of heat stress, and shortens the life of your equipment.
The good news is that a persistently hot kitchen is a solvable problem. Heat build-up is a symptom, and once you understand what your extraction and ventilation are meant to be doing, the causes are usually easy to spot. Below we walk through why kitchens overheat, how to tell whether your system is coping, and what genuinely brings the temperature back under control.
Every appliance on your line is a heat source, and the hotter and more open the cooking, the more thermal energy escapes into the room. Open-flame ranges and solid-fuel grills throw off far more convected heat than a covered electric griddle, which is exactly why the industry design guide, BESA's DW/172 Specification for Kitchen Ventilation Systems, assigns each appliance a thermal convection value based on its surface temperature and energy source. That value drives how much air the canopy above it must remove.
When a kitchen overheats, one of three things is usually happening:
For context, a comfortable working range for a commercial kitchen sits around 25°C to 28°C with relative humidity kept below roughly 60 per cent. Beyond that, staff tire faster and the space starts to feel oppressive. If you are routinely sitting above that band, the ventilation is not keeping pace with the cooking.
An extraction system can look perfectly healthy - fans humming, canopy in place - and still be moving a fraction of the air it should. The tell-tale signs are worth learning, because they point straight at the cause.
Watch for smoke and steam lingering under the canopy instead of being whipped away, condensation forming on walls and ceilings, cooking smells drifting into the dining room, and of course the heat itself. Grease dripping from filters or pooling at the canopy edge is a clear signal that capture has failed and deposits are accumulating where air should be flowing.
The reason cleaning matters so much is simple physics. Grease is sticky and it never stops arriving. As it lines the filters and the first run of ductwork, the free area for air to pass through shrinks, the fan has to work against greater resistance, and the volume it actually delivers falls away. Left long enough, a system that was designed to clear heat is barely ticking over - and, because that same grease is highly combustible, you have swapped a comfort problem for a fire risk. A thorough deep clean back to bare metal is frequently the single most effective step in getting a hot kitchen breathing again.
Extraction is only half the equation. Every cubic metre of hot air your canopy removes has to be replaced by fresh air coming in, and if there is no planned route for that replacement air, the kitchen fights itself. This is the part of the picture most overheating kitchens get wrong.
DW/172 recommends that make-up air be supplied at roughly 85 to 90 per cent of the volume being extracted. Get that balance right and the system flows smoothly - cool air enters at a controlled rate, absorbs heat from the equipment, and is drawn up and out by the canopy. Get it wrong and the room becomes negatively pressurised, as the extract fan strains to pull air the building cannot supply.
Negative pressure creates its own catalogue of misery. Doors become heavy to open, uncontrolled draughts whistle in through every gap, gas appliance flues can be disturbed, and - crucially - the extraction fan starts to underperform because there is simply not enough incoming air for it to move. The result is a kitchen that is both hot and stuffy, with an expensive canopy that cannot do its job. A properly designed make-up air supply, tempered in winter so you are not blowing cold air across the line, transforms the working environment. It is worth reading up on the role of make-up air in kitchen ventilation if this sounds familiar, because no amount of extra extraction will help until the replacement air is sorted.
Start with the cheapest, highest-impact move: get the system cleaned and measured. A deep clean of filters, canopy, plenum and ductwork restores the airflow you have already paid for, and a proper airflow check tells you whether the extraction rate matches the cooking underneath it. Very often, that alone brings the temperature back into a sensible range.
From there, work through the fundamentals in order:
The heat you feel on the line is not something you have to accept as the cost of running a kitchen. It is the visible result of a ventilation system that is either dirty, undersized, or starved of make-up air - and each of those has a clear remedy.
If the heat has crept up gradually over months, a build-up of grease is the most likely culprit and the first thing to rule out. If it has always been hot, look harder at capacity and make-up air. The hidden cost of a hot, poorly ventilated kitchen shows up in staff turnover, energy bills and equipment wear long before anyone measures a thermometer, so it pays to act early.
Questions
A comfortable working range for a commercial kitchen sits at roughly 25°C to 28°C, with relative humidity kept below about 60 per cent. There is no single legal maximum temperature under the Workplace (Health, Safety and Welfare) Regulations 1992, but employers must provide effective and suitable ventilation and a reasonable working environment. If your kitchen routinely runs hotter than that band, your extraction and make-up air are not keeping pace with the cooking.
Yes, and it is often the single most effective step. Grease steadily coats filters, canopy plenums and ductwork, narrowing the airway and forcing the fan to work against greater resistance, so the volume of hot air actually removed drops well below the original design figure. A deep clean back to bare metal restores that lost airflow, letting the canopy clear heat as intended - and it removes a serious fire risk at the same time.
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.