Electric Motor Heat Gain Calculator

When an electric motor and the equipment it drives both operate inside a conditioned space, essentially all of the electrical energy the motor draws ends up as heat in that space. The instantaneous sensible heat gain is calculated as Q = 2545 × (P / Eₘ) × Fᵤₘ × Fₗₘ, where P is the motor power rating in horsepower, Eₘ is the motor efficiency as a decimal fraction of 1.0 or less, Fᵤₘ is the motor use factor (the fraction of each hour the motor runs), and Fₗₘ is the motor load factor (the average load as a fraction of maximum horsepower). The constant 2545 is the conversion factor of BTU/h per horsepower (1 hp = 2,545 BTU/h). Dividing by efficiency accounts for the electrical input being larger than the mechanical output, since the difference is dissipated as heat. For example, a 5 hp motor at 90% efficiency running continuously at full load adds 2545 × (5 / 0.9) × 1.0 × 1.0 ≈ 14,139 BTU/hr. This formula applies to the common case where both the motor and the driven machine are located in the conditioned space.