Signs & diagnostics
Falling airflow is the common thread behind most of the warning signs - weak capture, lingering smoke, a hotter kitchen. Here is how a clogged extract run is diagnosed, from simple checks to a proper survey.
The short answer
Most of the warning signs in a kitchen extract system trace back to one thing: the airflow has dropped. When grease narrows the ductwork, the fan moves less air, and that single fact shows up as weak capture at the cookline, smoke that lingers, a kitchen that feels hotter, and a fan that sounds strained. Diagnosing a clogged run means recognising that these are not separate faults but one underlying problem - reduced airflow - and then confirming it, first with simple checks anyone can do and then with a proper survey.
The simple checks that point to a restriction
You can gauge airflow roughly without instruments. Hold a light tissue or slip of paper near a canopy edge or grille while the system runs: on a healthy system it is pulled firmly toward the opening; on a clogged one it barely moves. Watch how the cookline plume behaves - a strong system draws smoke and steam straight up, while a weak one lets them spread into the room. Notice the temperature: a kitchen that has become noticeably hotter during ordinary service is often one whose extraction is no longer carrying heat away.
These checks do not measure anything precisely, but together they build a consistent picture. If the tissue barely moves, the plume spreads, the kitchen is hot and the fan sounds strained, the diagnosis points strongly to a restriction in the run. What they cannot tell you is where the restriction is or how heavy it is - that is the job of a survey, which turns the impression of weak airflow into a located, measured finding.
Confirming and locating the clog
A survey confirms what the simple checks suggest and adds what they cannot. By opening access panels along the run and measuring grease deposits, a technician establishes where the duct has narrowed and by how much, checking the readings against the TR19 Grease benchmarks - a mean of two hundred microns between cleans, with five hundred microns or more at any point needing spot cleaning. That converts a vague sense of weak extraction into a clear map of the restriction.
Locating the clog matters because a restriction in one stretch drags down the whole system. Grease settles most where air slows - in bends, rises and long horizontal runs - so the survey concentrates on those points. Once the restriction is found and measured, cleaning it restores the free area, and the airflow the simple checks flagged as weak returns to the rate the system was designed for. Diagnosis and cure are the two halves of the same job.
What to do about it
Weak airflow is a prompt to survey the run, not to accept a hotter, smokier kitchen as normal. The simple checks tell you a restriction is likely; a survey confirms where it is and how bad, measured against the TR19 Grease limits; and cleaning the affected run restores the airflow. Because falling airflow underlies so many of the other signs, dealing with the restriction usually resolves several symptoms at once.
Questions
The simplest test is to hold a light tissue or slip of paper near a canopy edge or grille while the system runs. On a healthy system it is pulled firmly toward the opening; on a clogged one it barely moves. Combined with watching how the cookline plume behaves and noticing kitchen temperature, it gives a rough but consistent picture.
Extraction is a chain - the fan pulls air through the entire run, so a restriction anywhere reduces the airflow everywhere. Grease settles most in bends, rises and long horizontal stretches, and a heavy build-up in one of those points drags down capture at the cookline far away from it.
Yes - a make-up air shortage, a failing fan or a design fault can all weaken extraction. That is why a survey matters: it distinguishes a genuine grease restriction from an air-balance or mechanical issue, so the right fix is applied rather than assumed.
By opening access panels along the run and measuring grease deposits at several points, a technician establishes where the duct has narrowed and by how much, checking against the TR19 Grease limits. That turns a general sense of weak extraction into a located, measured finding.
If grease is the cause, clearing the affected run restores the free area and the airflow returns to the designed rate, usually resolving several symptoms at once. If weak airflow persists after cleaning, it points to a make-up air or mechanical issue that needs separate attention.
Phoenix Duct Clean · by the numbers
Weak airflow has a cause worth finding. We survey the run, locate the restriction and clean it so the system pulls at the rate it was designed for.