**Related Resources: calculators**

### Heat Gain from Electric Motors and their Loads Formula and Calculator

Heat Transfer Engineering and Design

Electric Motors Design and Engineering

Heat Gain from Motors and their Loads Formula and Calculator

Preview Heat Gain from Electrical Motors Calculators

Instantaneous rate of heat gain from equipment operated by electric motors within a space.

q_{em} = ( P / E_{M} ) · F_{UM} · F_{LM}

Where:

q_{em} = heat equivalent of equipment operation, kW

P = motor power rating, kW

E_{M} = motor efficiency, decimal fraction < 1.0

F_{UM} = motor use factor 1.0 or <1.0 (proportion operating)

F_{LM} = motor load factor 1.0 or <1.0

When motor is outside the conditioned space, but load is inside,

q_{em} = P · F_{UM} · F_{LM}

When motor is inside the conditioned space, but load is outside,

q_{em} = P [ ( 1.0 - E_{M} ) / E_{M} ] · F_{UM} · F_{LM}

Heat output of a motor is generally proportional to motor load, within rated overload limits.
Because of typically high no-load motor current, fixed losses, and other reasons, F_{LM} is generally
assumed to be unity, and no adjustment should be made for under loading or overloading
unless the situation is fixed and can be accurately established, and reduced-load efficiency data
can be obtained from the motor manufacturer.

Unless the manufacturer’s technical literature indicates otherwise, motor heat gain normally
should be equally divided between radiant and convective components for the subsequent cooling

load calculations.

Related:

- Electric Motor Definitions and Terminology
- Classification Electric Motors according to application, technology and NEMA
- Electric Motor Sizing Design Equations and Calculator
- Overall Heat Transfer Coefficient Table Charts and Equation
- Combined Overall Heat Transfer Coefficient Equation
- Convective Heat Transfer Coefficient - Heat Transfer
- Convective Heat Transfer Coefficients Table Chart
- Round Duct Heat Transfer Coefficient Wall Temperature Heat Transfer Equation and Calculator
- Overall Heat Transfer Coefficient Table Chart
- Overall Heat Transfer Coefficient Across Heat Exchanger Tubes Equation

Derived from resources provided by:

ASHRAE Pocket Guide for HVAC, 2013