Centrifugal Blower vs Side Channel Blower
Both move air. Their curves are shaped differently, and that single difference decides which machine belongs in your process — and which one will fail to do the job.
The one-line rule
Side channel for pressure. Centrifugal for flow. Everything else is detail.
A side channel blower is a low-flow, high-pressure machine for its size. A centrifugal blower is the opposite: it moves a large volume of air but develops modest pressure. The two are confused constantly, usually with expensive results, because the published numbers overlap — you can find a side channel unit and a centrifugal unit quoted at the same airflow, and they will still do completely different jobs.
The reason is the shape of the curve. A side channel curve is relatively flat: as resistance rises, flow falls only gradually, so the machine keeps working against a heavy system. A centrifugal curve falls steeply: add resistance and the flow collapses. That single geometric difference decides which technology fits.
Head-to-head comparison
Eight criteria that cover the decision in almost every case.
| Criterion | Side channel blower | Centrifugal blower |
|---|---|---|
| Pressure capability | Up to roughly 0.75 bar | To about 1 bar in high-speed designs, lower in standard fan builds |
| Flow at a given size | Low to moderate | High to very high |
| Curve shape | Flat — stable against rising system resistance | Steep — flow falls sharply as pressure rises |
| Efficiency at duty point | Good in its pressure band; falls off if run far from the rated point | Very good when the duty point sits near its design flow |
| Noise | Moderate; silencers are effective | Generally louder at high flow; needs acoustic treatment at large sizes |
| Size and weight at equal duty | Compact | Larger for the same pressure |
| Maintenance | Filter changes, occasional bearings | Belt drive on many models, so belts and bearings are consumables |
| Best for | Aeration, vacuum lifting, pneumatic conveying, air knives, drying | Ventilation, dust collection, combustion air, large-volume conveying, aeration at scale |
Both technologies appear in the aeration and conveying markets at different plant sizes — which is why the choice is made on flow, not on category.
When side channel wins
These duties are where a centrifugal machine either cannot reach the pressure or is simply the wrong tool.
- Anything requiring more than about 200 mbar of pressure or vacuum at modest flow
- Vacuum lifting and hold-down tables, where the machine must hold vacuum against leakage
- Air-knife drying on packaging and printing lines — pressure and velocity matter more than volume
- Pneumatic conveying over short distances with dense or granular material
- Aeration for ponds, aquaculture and small treatment plants
- Installations where floor space is scarce and the unit must sit inside the machine it serves
When centrifugal wins
Above a certain flow, a centrifugal machine stops being the alternative and becomes the only sensible answer.
- Large air volumes at low to moderate pressure — ventilation, dust collection, cooling, combustion air
- Continuous duty where efficiency at the design flow dominates the running cost
- Applications where the system resistance is stable and known, so the steep curve is an advantage rather than a risk
- Processes needing airflow to vary across a wide range, which a frequency inverter handles well on a dynamic machine
- Large aeration plants, where multi-stage centrifugal designs deliver the flow at aeration pressure
Where Roots fits — the third option
There is a pressure-and-flow region where neither of the above is the right machine, and that is where the Roots blower sits.
A Roots blower is positive displacement: two lobes rotate inside a casing, trapping and displacing a fixed volume with each revolution. The consequence is that flow stays nearly constant as pressure rises — the opposite behaviour to a fan. That makes it the default choice for wastewater aeration, gas boosting and pneumatic conveying, from about 0.5 bar upward, and we build them from 0.55 to 355 kW.
The trade-off is noise and heat: a Roots machine is noticeably louder than a side channel unit at the same duty, and needs an acoustic enclosure indoors. If your application sits below roughly 0.5 bar, a side channel or centrifugal machine will usually be quieter, smaller and cheaper to buy.
What actually decides the energy bill
The nameplate power is not the running cost. The efficiency at your duty point is.
Two blowers rated at the same kW can differ by 15–25 % in the electricity they consume doing the same job, because the nameplate figure is a maximum, not an operating point. What matters is where your duty point falls relative to the machine's best efficiency region, and whether the motor is IE3 class or better.
On a machine that runs 6 000 hours a year, that difference is the largest single line in the total cost of ownership — larger than the purchase price. Ask for the curve at your duty point and the motor efficiency class, and compare those two numbers before you compare prices.
Frequently Asked Questions
Which is better, a centrifugal blower or a side channel blower?
Neither is better in general — they solve different problems. A side channel blower produces higher pressure at lower flow and stays stable when system resistance rises, so it suits vacuum lifting, air knives, drying and short-distance conveying. A centrifugal blower produces far more flow at lower pressure, so it suits ventilation, dust collection, combustion air and large-scale aeration. Choose on the duty point.
Can a centrifugal blower replace a side channel blower?
Only if the replacement can reach your required pressure at your required flow. Many centrifugal fans top out well below the pressure a side channel blower produces, and because their curve is steep they lose flow quickly as resistance increases. Ask for the curve at your duty point before substituting.
Why does a side channel blower hold flow better as pressure rises?
Because of the regenerative principle. Air is recirculated through the impeller vanes many times along the annular channel, and energy is added at each passage, so the machine keeps building pressure instead of stalling as resistance increases. That produces the characteristically flat curve.
When should I choose a Roots blower instead?
Above roughly 0.5 bar, or wherever you need nearly constant flow that does not fall off as pressure rises. Wastewater aeration, gas boosting and dense-phase pneumatic conveying are the classic duties. The price is noise and heat: a Roots machine needs acoustic treatment indoors.
Does a frequency inverter work with both types?
Yes, and on both it is usually the single best energy-saving measure, because airflow scales with speed while power scales with roughly the cube of speed. Tell us at enquiry stage that a VFD will be fitted — the speed range affects the mechanical limits and the motor derating, and it is cheaper to allow for it during selection than afterwards.
Send Us Your Duty Point
Airflow, pressure or vacuum, voltage and application are enough for us to come back with a model and a price — within 24 hours.
