Heat, energy & performance
It starts fine and turns oppressive as the rush builds. A stuffy kitchen at mid-service is usually an extract that cannot keep up: as every appliance fires, the heat, steam and combustion products outpace a canopy that has lost capture to grease. The margin that carried the quiet period runs out.
The short answer
It starts fine and turns oppressive as the rush builds. A stuffy kitchen at mid-service is usually an extract that cannot keep up: as every appliance fires, the heat, steam and combustion products outpace a canopy that has lost capture to grease. The margin that carried the quiet period runs out.
The detail
At the start of service only some appliances are running, so even a slightly under-performing extract can cope. The heat plume is modest and the canopy still captures most of it. The room feels reasonable, which is why an airflow problem often hides until the kitchen is under real load.
As the rush arrives, every burner, oven and fryer is working at once. The combined plume - hot air, steam off boiling and blanching, and combustion products from gas - rises far faster than in the lull. Now the canopy needs its full design capture velocity to contain it.
A greased extract does not have that margin. Resistance from loaded filters and duct has cut the airflow, so at peak load the capture velocity is no longer enough. The plume overspills into the room, humidity climbs, and the space that felt fine at five o clock is oppressive by eight.
Humidity is a big part of the stuffiness. HSE lists it as one of the six thermal comfort factors, and a kitchen throwing off steam that the extract cannot clear feels far hotter than the air temperature alone suggests. The body cannot shed heat efficiently in humid air, so staff feel it quickly.
What it means for you
If the kitchen is comfortable early and stifling at the rush, suspect the extract before the thermostat. The pattern - fine at low load, failing at high load - is the signature of a system that has lost its capture margin, and grease is the usual reason the margin disappeared.
Restoring airflow restores the margin. A TR19 clean of filters, plenum, duct and fan brings the capture velocity back to its design figure, so the canopy can contain the full peak plume again and the room stays workable through the busiest hour.
Phoenix Duct Clean measures and clears grease across the whole system, so the recovery holds at peak load - not just in the quiet spells when almost any extract can cope.
The service behind the guide
Sibling guides
Poor extraction and air-con cost · Staff comfort and productivity · Dark kitchen shared canopies
Questions
At low load a weak extract can cope, but at peak every appliance fires at once and the plume needs full capture velocity. A greased system has lost that margin, so it overspills into the room exactly when the load is highest.
Both. Steam from cooking is a big contributor, and HSE lists humidity as one of six thermal comfort factors. Humid air stops the body shedding heat, so a steamy kitchen feels far hotter than the air temperature alone.
Rarely. If the system was sized correctly at commissioning, the problem is usually lost airflow from grease rather than fan capacity. Cleaning the restriction restores the original performance without changing the plant.
Grease raises resistance and cuts the extract volume. At low load the reduced airflow still copes; at peak the plume is far larger, so the shortfall in capture velocity finally shows as overspill and stuffiness.
If lost capture is the cause, yes. A TR19 clean returns the fan to design airflow, so the canopy can contain the full peak plume again and the room stays workable through the busiest part of service.
Phoenix Duct Clean · by the numbers
Lost capture at peak load is usually grease. Book a TR19 clean to get the margin back.