The efficiency of electric motors isn’t the most exciting topic, but it significantly affects your electric bill. Efficiency can be calculated by dividing an electric motor’s power output (in Watts) by its power consumption.
The efficiency of common (not all motors) electric motors varies broadly from a measly 10% to 95% efficiency. Being a transducer that converts electrical energy to mechanical energy, you’ll need the best efficiency you can get.
A simplified way to distinguish motors is by their type. Shaded-pole motors (which are reliable and affordable, so they’re not inherently bad) are usually between 10% and 20% efficiency, Permanent split capacitor start motors range from 40% to 60%, and universal motors are also in the 40% efficiency range.
Three-phase AC motors can achieve efficiency levels above 90%. Electronically commutated motors (ECM) can achieve very high efficiency levels over 80% as well.
Brushed DC motors can achieve reasonably high efficiency as well, but their brushless counterparts (BLDC) are quieter, more efficient and less susceptible to mechanical issues due to the lack of brushes.