Duct fan ratings compare within a brand, not across
Almost nobody gives a test distance or names a standard. AC Infinity's "Total Noise" and VIVOSUN's "Noise Level" come with neither. TerraBloom is the single exception, and its 8 inch silenced fan reads "31-51 dBA (measured ducted at 6-ft from inlet)", the most explicit measurement note in the category.
Three consequences follow. Inside one brand the comparison holds, and AC Infinity's table shows its cheaper A6 is louder with less airflow than the S6. Between two makers, a gap of a few dBA proves nothing, since each brand tests in its own way. And the printed figure describes full speed, which is not how anyone runs these fans: every EC fan here ships with an 8 or 10 speed controller, while VENTS is alone in saying what a lower speed sounds like.
Those VENTS figures are sones, a loudness unit the Home Ventilating Institute uses for fans, where one sone is roughly a quiet refrigerator. Turning sones into dBA at a distance takes assumptions the maker does not state, so the Turbo Tubes rank in a separate lane. Our sones explainer covers the difference.
Bathroom fans are rated in sones too. The bathroom exhaust fan guide shows how that figure moves with duct size and static pressure.
Is AC Infinity's T series quieter than the S series?
No. For each duct size the S and T fans publish identical Total Airflow, Total Noise and wattage. The T costs $29 to $50 more, and the premium buys a controller with temperature, humidity and VPD triggers. If quiet airflow is the whole job, buy the S and keep the difference.
The A series is where cheaper costs you. The A6 sells for $9 less than the S6 and is rated "34 dBA" at "352 CFM", against the S6's "30 dBA" at "425 CFM", so it is louder per CFM by AC Infinity's own table.
AC Infinity also makes AIRLIFT shutter fans, which it lists for attics among other rooms. Their A-weighted figures, 62 to 68 dBA, sit in our guide to the quietest attic fans, kept apart from the plain dB and sone ratings other attic fan makers print.
Bigger fans rate louder at full speed
The 8 inch S8 rates "38 dBA"; the 6 inch S6 rates "30 dBA". Size costs decibels on the spec sheet, though a bigger fan run slower stays below its rating.
| Fan | Duct | Noise as printed | Airflow |
|---|
| AC Infinity CLOUDLINE S4 | 4 inch | 26 dBA | 226 CFM |
| VIVOSUN AeroZesh T4 | 4 inch | 28 dBA | 210 CFM |
| iPower 4 inch EC | 4 inch | 29 dB (Amazon listing) | 214 CFM |
| AC Infinity CLOUDLINE S6 | 6 inch | 30 dBA | 425 CFM |
| TerraBloom ECMF-150-S | 6 inch | 31-50 dBA across speeds | 288 CFM |
| VIVOSUN AeroZesh T6 | 6 inch | 32 dBA | 408 CFM |
| AC Infinity CLOUDLINE A6 | 6 inch | 34 dBA | 352 CFM |
| AC Infinity CLOUDLINE S8 | 8 inch | 38 dBA | 857 CFM |
| VIVOSUN AeroZesh T8 | 8 inch | 45 dBA | 832 CFM |
Six inches is the survey's key size, and there the S6 leads on both columns. The T6 trails it by two decibels and 17 CFM. TerraBloom gives up a third of the airflow for its foam lining and still tops out at 50 dBA.
When space and budget allow, buy one size up and run it slower. An 8 inch fan at half speed moves 6 inch air at less than its rated noise. Only the VENTS PDF puts a published number on that effect, with its TT 100 dropping from "2.5" sones on high to "1.1" on low.
Vortex, Hurricane, Hon&Guan and Fantech are left out
Vortex was the inline fan every ventilation forum recommended for a decade. It now sits under Panasonic's Atmosphere brand, and neither the official submittal sheet nor the Atmosphere catalog PDF gives a noise figure for the inline fans; the only dBA number in that catalog belongs to an unrelated destratification fan. Retailers quote "11.3 sones" for the VTX600. No maker page we could retrieve backs that up, so Vortex is out.
Hurricane, a Hydrofarm brand, lists CFM, RPM, watts and a warranty on its site and on Hydrofarm's pages, and no noise figure at all. Hon&Guan's silenced fans carry numbers only inside marketing images. Fantech's spec pages would not render outside scripts, and its PDF links returned errors.
None of the four is approximated. The same rule kept unrated leaders out of our paper shredder and litter box guides.
iPower is the reverse case: no working website, so its figures are quoted from Amazon brand listings and flagged as the weakest sourcing on the page.
How do you make an inline duct fan quieter?
Turn it down first.
Then decouple it. Hanging the fan from the joists on rubber or spring isolators, and keeping a bend or a stretch of insulated flex duct between the fan and the room, usually does more than the two decibels that separate rival fans on a spec sheet. Mounting is half the noise, and two makers concede as much in their engineering. AC Infinity sells noise reduction clamps as an accessory and gives the A series a vibration damping plastic base. TerraBloom hangs its silenced fans on four internal suspension springs inside 2 inches of acoustic foam.
That lesson transfers to any fan on this page.
