Interactive Calculator · 2026
Blower Size Calculator
Size the aeration blower for a sewage treatment plant. Enter the air flow and discharge head, and get the shaft power in kW, the motor rating in HP and a recommended standard motor — the numbers every blower specification starts from.
Shaft power → recommended motor rating (kW)
Blower duty
Free air delivery required at the diffusers.
Diffuser submergence + pipe and header losses.
Overall wire-to-air efficiency of the blower package — positive-displacement units typically sit at 55–65%.
Shaft power vs recommended motor
Both shown in kW so you can see the ≈15% margin built into the standard motor rating.
The blower absorbs about 6.81 kW at the shaft. A driving motor is never picked at exactly that figure — you add a service margin and round up to the next standard frame.
Here that lands on a 11 HP motor (≈8.2 kW), leaving headroom for start-up, fouling and warm-day air density.
How this is calculated
- Air flow = 5 m³/min ÷ 60 = 0.08 m³/s.
- Pressure rise = 5 m × 9,810 Pa/m = 49,050 Pa.
- Shaft power = (air flow × pressure) ÷ efficiency ÷ 1,000 = (0.08 × 49,050) ÷ 0.60 ÷ 1,000 = 6.81 kW.
- Motor HP = 6.81 kW × 1.341 = 9.14 HP.
- Recommended motor = ceil(9.14 HP × 1.15) = 11 HP.
Indicative sizing for concept planning. A detailed design must also fix air temperature, altitude, diffuser type and control turndown — confirm with a qualified consultant before procurement.
Related Guides — Deep-dive reading
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