Centrifugal Blower vs Centrifugal Fan: What the Words Mean and Why It Matters

People use “blower” and “fan” interchangeably, and in everyday plant conversation that is usually fine. But the two words have a formal engineering definition, and the difference explains why a machine that industry calls a blower can be a “fan” on the datasheet. If you write specifications, compare quotations, or search for equipment, it helps to know what each word means, where the boundary sits, and how to avoid ambiguity by quoting pressure in plain units.

The Formal Definition: Pressure Ratio

The formal distinction uses the pressure ratio, which is the absolute pressure at the outlet divided by the absolute pressure at the inlet. Under the ASME convention:

Machine	Pressure ratio	Pressure rise at atmospheric inlet
Fan	Up to 1.11	Up to about 11.1 kPa (about 1,130 mm WC)
Blower	1.11 to 1.20	About 11.1 to 20.3 kPa (about 1,130 to 2,070 mm WC)
Compressor	Above 1.20	Above about 20.3 kPa

The reason for the boundaries is compressibility. At low pressure ratios, air behaves almost as if its density does not change as it passes through the machine, and simple fan calculations are accurate. As the ratio rises, the density change matters more, the calculations need correction, and the machine starts to behave more like a compressor.

Where Our Blowers Fall

Our standard maximum is 500 mm WC, about 4.9 kPa, a pressure ratio of about 1.048. The table shows how a few pressures compare.

Static pressure	Pressure ratio
100 mm WC (981 Pa)	1.010
200 mm WC (1,961 Pa)	1.019
500 mm WC (4,903 Pa)	1.048
about 1,130 mm WC (11.1 kPa)	1.110
about 2,070 mm WC (20.3 kPa)	1.200

On the formal definition, everything up to 1,130 mm WC is a fan, so a 500 mm WC centrifugal machine is a high-pressure centrifugal fan. That is a correct description, and it also happens that almost nobody calls it that.

How Industry Actually Uses the Words

On the plant floor and in catalogues, “blower” usually means a centrifugal fan built for higher pressure than an ordinary ventilation fan. The same machine may be called a blower, a high-pressure fan, a pressure blower, or an industrial fan, depending on the supplier and the country. Buyers searching for equipment often type “centrifugal blower” for machines that the ASME definition would call fans, so both words are useful for finding what you need.

There is also a practical split in the market: blowers are commonly divided into centrifugal and positive-displacement types. Positive-displacement blowers, such as rotary lobe machines, work by trapping a fixed volume of air and moving it, and are built for higher pressure at lower flow. See centrifugal versus positive-displacement blowers.

Why the Distinction Still Matters

Calculation accuracy. Below a ratio of 1.11, treating air as incompressible gives good results. Above it, compressibility corrections apply. For our range, at a ratio of about 1.05, the simple methods in these guides are appropriate.

Standards and testing. Fans and blowers are tested to standards such as ISO 5801 and AMCA 210, and the way results are reported reflects the pressure range. See blower performance testing.

Comparing quotations. One supplier’s “blower” at 400 mm WC may be another’s “fan.” Compare on the pressure, the flow, and the pressure basis, not on the name.

Regulations. Efficiency and ecodesign rules often define their scope by machine type, power, and pressure. For example, the EU fan regulation covers fans between 125 W and 500 kW, which places an 800 HP machine (about 597 kW) above its upper limit.

Absolute Pressure, Altitude, and the Ratio

The pressure ratio is calculated from absolute pressures, so the site’s atmospheric pressure matters. A blower that develops 4.9 kPa at sea level, where the inlet is at about 101.3 kPa, has a ratio of about 1.048. At a site 2,400 m above sea level, where atmospheric pressure is about 75.9 kPa, the same pressure rise is a ratio of about 1.065, because the inlet pressure is lower. The ratio is still well below 1.11, so the machine remains a fan by the formal definition, but the example shows why the definition is about ratio and not about a fixed number of pascals. In practice, for the pressures in our range, the difference does not change how the machine is selected or sized.

The Safe Way to Specify

Avoid depending on the word. Instead, give:

1. Airflow in m³/h or m³/s, stating whether it is actual or standard.
2. Pressure in mm WC or Pa, stating whether it is static or total.
3. Gas conditions: temperature, altitude, humidity, and composition.
4. Application: so the supplier can judge the wheel type and construction.

With those four items, it does not matter whether the machine is called a fan or a blower.

A Note on Compressors

Above a pressure ratio of about 1.20, the machine is a compressor by the formal definition. Some multistage centrifugal machines and high-speed geared machines reach those pressures, but they are a different class of equipment with different cost, controls, and cooling. Our range does not extend there, and duties above 500 mm WC are better served by other machine types.

Where Our Range Fits

NextAir Systems manufactures centrifugal blowers up to 800 HP (about 597 kW) and up to 500 mm WC (about 4.9 kPa) static pressure, with backward-curved and forward-curved wheels and single-inlet and double-inlet designs. We call them blowers in the common industrial sense and state pressure in mm WC so that there is no ambiguity.

Send Us Your Duty

Tell us your airflow, pressure, and gas conditions, and we’ll confirm whether a centrifugal blower suits the duty. Contact us for a free quote.

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