Diagnostics & problems
It seems backwards: the system sounds like it is working harder, yet it captures less. A rise in noise with a fall in capture is a specific and useful fault signal, not a sign of extra power. Here is what it usually means.
The short answer
If your extraction has grown noticeably noisier while capturing less, resist the instinct to read the noise as effort. A system does not get stronger by getting louder. New or rising noise alongside falling capture is a recognisable pattern that points to a restriction, wear or a leak, and it is one of the more useful signals a system gives you because it tells you where to look.
The detail
Air moving through a healthy system is relatively quiet. Introduce a restriction, a loading filter, a partly blocked duct, a closed or misplaced damper, and air is forced through a smaller gap at higher local velocity, which creates turbulence and a whistle or roar exactly at the restriction, even as total flow through the system drops. A clogging filter is the classic case: the pressure drop across it climbs, the fan cannot overcome it, and the whole system moves less air while sounding busier.
Mechanical wear makes its own noise. Perished or slipping fan belts squeal and slip, so the impeller turns more slowly than it should while sounding strained. Tired bearings rumble and grind. A worn, corroded or dust-caked impeller runs rough and out of balance. And loose or split ductwork rattles and hisses as air leaks through gaps, which both makes noise and bleeds away the pull that should reach the hood. In each case the ear is picking up energy being wasted rather than work being done.
What it means for you
A change in sound is a good reason to measure, because the numbers separate the causes the ear cannot. A thorough examination reads airflow and static pressure at the hoods, along the duct, across the filter and across the fan, and compares each to the commissioned datum. Hood static pressure in particular tracks hood airflow, so a shift from the design figure flags a blockage, a leak or a loaded filter quickly. Rotation, belts, bearings and the impeller are checked at the same time.
The trap to avoid is treating a felt or heard draught as proof of control. You can hear plenty of air movement and still be below the velocity needed to capture contaminant at the source, particularly if the sound is turbulence at a restriction rather than clean flow into the hood. That is why the test measures capture at the point of release, not just the noise or the breeze. The sound tells you something changed; the meter tells you what, and whether people are still protected.
The service behind the guide
We treat a change in noise as a symptom to measure, not to guess at. Our examination reads airflow and pressures against the commissioned figures and checks the fan, belts and ductwork to find the fault behind the sound.
Questions
Usually because of a restriction, wear or a leak. A blocked filter or duct forces air through a smaller gap at higher local velocity, creating noise while total flow drops. Slipping belts, worn bearings and leaking ducts all add noise while wasting airflow.
No. Extra noise is often wasted energy, not extra capture. Turbulence at a restriction, a straining belt or a rattling leak can all sound busier while the system moves less air than it was designed to.
Not as proof of control. You can feel and hear air move and still be below the velocity needed to capture contaminant at the source. Capture has to be measured at the point of release, not judged by the breeze.
By measuring airflow and static pressure at the hoods, along the duct and across the filter and fan, and comparing each to the commissioned figures. Hood static pressure quickly flags blockages, leaks and loaded filters.
A change in noise with reduced capture means the system is drifting from its design and may no longer be controlling exposure. It should be examined promptly rather than left, because the fault behind the noise tends to worsen.
Phoenix Duct Clean · by the numbers
A change in sound is a lead worth following with a meter. We measure airflow and static pressure against the commissioned figures to find the fault behind the noise. Call to book the test.