Motor Efficiency Classes IE3 and IE4 for Blower Drives: What a Class Step Is Worth

By the NextAir Systems engineering team. Last reviewed October 2026.

Motor efficiency classes look like a small print item on a blower quotation, and the arithmetic says otherwise. The motor is the last link between the grid and the air, and for a machine running thousands of hours a year, a class step is real money.

IEC 60034-30-1 defines the classes. The useful trick is that each step is best understood as a reduction in losses, not an increase in efficiency. Once you see it that way, the value of a class step is a short calculation, and the break-even price premium falls out.

The short version

• IEC 60034-30-1 defines harmonised efficiency classes for single-speed motors from 0.12 to 1,000 kW. IE3 is Premium and IE4 is Super Premium, and each class step cuts losses by roughly 20%.^[1]
• For a 4-pole 50 Hz 15 kW motor the nominal full-load efficiency is 92.1% in IE3 and 93.9% in IE4, a gain of 1.8 points that removes close to a quarter of the losses.^[1]
• For a 110 kW motor running 8,000 hours a year, a 20% loss reduction saves about 8,293 kWh, worth USD 663 a year at USD 0.08 per kWh, in the example below.
• Variable speed drives must meet drive efficiency class IE2 under IEC 61800-9-2, which is a separate item from the motor class.^[1]

Classes as loss reductions

IEC 60034-30-1 sets efficiency classes for single-speed motors across a wide range, tested to IEC 60034-2-1. The classes run IE1 to IE4, with IE3 called Premium and IE4 Super Premium. A fact that is often missed is that each step reduces the motor’s losses, the heat it makes, by roughly 20%.^[1] Efficiency in percentage points looks like a tiny change, and loss is the real quantity.

The published figures for a 15 kW four-pole 50 Hz motor show it: 92.1% in IE3 and 93.9% in IE4.^[1] The loss at 15 kW output is 15 × (1 ÷ 0.921 − 1) = 1.29 kW in IE3 and 15 × (1 ÷ 0.939 − 1) = 0.97 kW in IE4. That is a reduction of 25%, and the class step is nominally 20%, so the two agree within the rounding of the published efficiencies.

What a class step is worth for a blower

The table works out the loss and the saving for four motor sizes at 8,000 hours a year and USD 0.08 per kWh. The 15 kW IE3 efficiency is the published figure.^[1] The others are assumptions chosen to be plausible for IE3 motors of that size, and the IE4 values are derived by applying the 20% loss reduction. Check them against the motor datasheet for your project.

Motor (kW)	IE3 efficiency (%)	IE4 efficiency (%)	IE3 loss (kW)	IE4 loss (kW)	Loss saved (W)	Energy saved (kWh/year)	Value (USD/year)	Present value over 15 years (USD)
15	92.1	93.9	1.29	0.97	312.2	2,498	200	1,710
55	94.6 (assumed)	95.6 (derived)	3.14	2.51	627.9	5,023	402	3,440
110	95.5 (assumed)	96.4 (derived)	5.18	4.15	1036.6	8,293	663	5,679
250	96.0 (assumed)	96.8 (derived)	10.42	8.33	2083.3	16,667	1,333	11,412

Worked example. For the 110 kW motor, the IE3 loss is 5.18 kW and the IE4 loss is 4.15 kW. The difference of about 1036.6 W, running 8,000 hours, is 8,293 kWh a year, or USD 663. Over 15 years at an 8% discount rate the present value is about USD 5,679. That figure is the break-even premium: if an IE4 motor costs less than that extra, it pays for itself, ignoring any cooling or reliability benefit.

The break-even premium is the number to ask for. Do not ask whether IE4 is worth it in general. Ask what the IE4 premium is for this motor, and compare it with the present value of the saving. The relationship between hours and payback is the same one explained in the life-cycle cost article.

Where the benefit shrinks

• Low running hours. The saving scales directly with hours. A motor that runs 1,000 hours a year saves an eighth of the figure above.
• Part load. Motors are most efficient near full load. At 30% load for 2,000 hours a year, early replacement may not pay at all, as the same source notes.^[1]
• Large motors. The gap between IE3 and IE4 in efficiency points narrows as size grows, though the absolute loss saved in kW can still be large.
• Variable speed. If the blower is controlled by speed, the motor runs at part load most of the time, which changes the case. See flow control for blowers.
• Starting duty. High-inertia blowers can stress some high-efficiency designs, because they often have lower starting torque or higher inrush. Check the starting method, as in motors, drives and starting.

Reliability is part of the case

Efficiency is not the only reason people specify the higher classes. A motor that wastes less energy as heat runs cooler, and winding insulation life is strongly temperature dependent. Sulzer’s technical article notes the rule of thumb that insulation life roughly doubles for each 10 K drop in operating temperature, and that a more efficient motor can therefore bring a longer operating life.^[2] For a blower on continuous duty in a hot plant room that is worth weighing alongside the energy figure, though it is harder to put a number on. Ask the supplier for the temperature rise class and the thermal reserve of the motor you are offered.

What to ask for

1. The motor class and nominal efficiency at full load, and at 75% and 50% load.
2. Rated power, number of poles, voltage and frequency.
3. Test standard for the efficiency figure.
4. Price premium for the next class up, so you can compare it with the present value of the saving.
5. Efficiency of the drive, if a VFD is used. Drives are classed separately, and IEC 61800-9-2 sets IE2 as the class a variable speed drive must meet.^[1]

Where this fits with NextAir

NextAir blowers are supplied with motors and VFDs bought out from established manufacturers, and we can quote IE3 or IE4 and show the break-even premium. Send your duty and hours to our centrifugal blower manufacturer team. Our centrifugal blower guide covers the range, and cement plants is a typical high-hours duty.

Sources

1. Fabrico (summary of IEC 60034-30-1). IE3 vs IE4 motors: efficiency classes explained (IEC 60034-30-1).
2. Sulzer. A lifetime of efficiency (technical article on IE3 motors).

Figures and tables on this page are calculated or compiled by NextAir Systems and you are welcome to reuse them with a link back to this article.

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