Signs & diagnostics
A well-maintained extract system pulls smoke and steam away almost as fast as the cookline produces them. When smoke starts hanging around, it is a sign the ductwork behind the canopy has clogged.
The short answer
A commercial extract system is sized to capture smoke, steam and heat at the cookline and carry them away almost as fast as they are produced. When smoke starts to linger - hanging above the equipment, drifting past the canopy line, or filling the kitchen during ordinary cooking - it means the system is no longer moving air the way it should. The most common reason is grease narrowing the ductwork behind the canopy, so the fan cannot pull the volume needed to clear the smoke. The lingering haze is a visible warning that the concealed run has clogged.
Why a clogged duct lets smoke hang
Extraction works as a chain: the canopy captures the plume, the ductwork carries it, and the fan drives the whole thing. Grease deposits reduce the free area inside the duct, so the same fan effort moves less air. That drop is felt right back at the cookline - the canopy pulls less, capture weakens, and smoke that would once have been drawn straight up instead spreads into the room before it clears.
Because the restriction is inside the ductwork, the cause is invisible while the effect is obvious. Staff notice the kitchen feels hazier and hotter, but the grease doing it sits out of sight above the ceiling. In some cases the reduced airflow lets smoke reach a detector that would normally stay clear, triggering false alarms - another sign that the system is no longer handling the smoke load it should.
What the lingering smoke signals
The value of lingering smoke as a sign is that it makes an invisible problem visible. You cannot see grease building inside the duct, but you can see smoke failing to clear - and the two are directly linked. When the haze appears during normal cooking rather than a one-off heavy session, it is telling you the extract route has lost enough free area that capture has genuinely dropped, not just been briefly overwhelmed.
There is a safety edge to this too. The same grease that is choking the airflow is a combustible load, and a kitchen where smoke lingers is often a kitchen where the fire risk in the duct is climbing at the same time. So lingering smoke is worth reading as two warnings in one: capture has failed, and the reason it failed is the very deposit that raises the fire risk.
What to do about it
Lingering smoke is a prompt to look inside the ductwork rather than to prop doors open and put up with the haze. A survey finds where the run has restricted, and cleaning the ductwork and fan restores the free area the system needs to pull smoke away at source. Once the airflow is back, capture returns to the cookline and the smoke clears the way it did when the system was new.
Questions
It can be - a kitchen starved of replacement air cannot extract properly even with a clean duct. But grease narrowing the ductwork is a very common cause, and the two often go together. A survey distinguishes a genuine restriction from an air-balance issue so the right fix is applied.
The same reduced airflow that lets smoke hang also fails to carry heat away, so the kitchen warms up. Rising temperature and lingering smoke usually appear together because both are symptoms of the same loss of extraction performance.
Sometimes. When airflow drops, smoke that would normally be drawn away can reach a detector and trigger a false alarm. Repeated nuisance alarms during ordinary cooking are worth treating as a sign the extract system is no longer clearing smoke as it should.
Lingering smoke is not a fire, but it points to a grease load that is both choking the airflow and adding to the combustible load in the duct. It is a signal the system is falling behind on two fronts at once, so it should be surveyed rather than tolerated.
If grease is the cause, clearing the ductwork and fan restores the free area and capture returns quickly. If smoke still lingers after a clean, it points to a design or make-up air issue that needs separate attention rather than more cleaning.
Phoenix Duct Clean · by the numbers
Lingering smoke means the run has restricted. We survey the ductwork, find where the airflow is choked and clean it so the system captures and clears the way it was designed to.