Diagnostics & problems
Some systems never worked. Not worn out, not neglected: simply built too small for the job from day one. An undersized system fails even when it is clean and serviced, because the fault is in the design, not the maintenance.
The short answer
Not every failing extraction system is a worn one. Some were never capable of controlling the exposure they were installed for: built with a fan too small, a hood too small or badly placed, or ducts that were never going to move enough air. An undersized system is different from a degraded one because servicing does not fix it. Change the filter, service the fan, tighten every joint, and it still lets contaminant escape, because the shortfall is in the design, not the condition.
The detail
A few patterns give it away. There is always some escape, smell or settled dust, even right after maintenance and even with a clean filter. Capture only works with the source pressed almost against the hood mouth, and falls away sharply the moment the work moves back, a sign the hood is too small or too far and the capture velocity was never adequate. Symptoms and complaints trace back not to a recent change but to the very beginning, from the day the system was commissioned. And a look at the paperwork often confirms it: the commissioning report shows figures that were marginal or below the design target at handover, or there is no commissioning data at all because the system was never properly proven.
The underlying causes sit in the specification. An undersized fan cannot overcome the system's resistance while still holding capture velocity at the hood, so it moves air but never enough at the point that matters. A hood that is too small, the wrong type or too far from the source cannot form a capture zone that reaches the contaminant. Ducts that are too small or too long throttle the flow before it ever gets to work. And a system whose replacement air was never planned is starved from the outset. Any one of these leaves a system that is busy but not effective.
What it means for you
The important consequence is that you cannot maintain your way out of a design shortfall. Pouring money into servicing an undersized system buys nothing, because every service returns it to a baseline that was never good enough. A thorough examination benchmarks the system against what the work actually requires and against recognised good practice, so it can distinguish a system that has drifted from one that never reached the standard, and say so plainly rather than passing it as merely dirty.
Where the examination finds a genuine design shortfall, the honest answer is redesign or replacement of the inadequate elements, a bigger or better-placed hood, a fan sized to the real demand, proper replacement air, rather than another round of maintenance. It is worth knowing early, because an undersized system quietly exposes people for its entire life while looking, to anyone judging it by the running fan, as though it is doing its job.
The service behind the guide
We benchmark your system against what the job needs and against good practice, so a design shortfall is named as one rather than passed off as dirt, and you know whether to service, rebalance or redesign.
Questions
The tell is failure that maintenance does not cure: some escape, smell or dust even when the system is clean and freshly serviced, capture that only works with the source against the hood, and problems that trace back to commissioning rather than to a recent change.
Because the fault is in the design, not the condition. Every service returns the system to a baseline that was never adequate, so a clean, well-maintained but undersized system still fails to control exposure.
Commonly an undersized fan that cannot hold capture velocity while overcoming resistance, a hood too small, wrong or too far from the source, ducts too small or too long, or replacement air that was never planned.
A thorough examination benchmarks performance against what the work needs and against recognised good practice. Wear shows as a drop from a previously adequate baseline; undersizing shows as a system that never reached the standard.
Redesign or replacement of the inadequate elements, a larger or better-placed hood, a fan sized to the real demand, and proper replacement air, rather than further maintenance that cannot raise the baseline.
Phoenix Duct Clean · by the numbers
If extraction fails even when clean and serviced, the design may be the problem. Call to book an examination that benchmarks performance against what the job actually needs.