Formula variables
- kW is the heater power used for the estimate.
- V is the selected nominal voltage.
- Phase selects the single-phase or balanced three-phase equation.
- The formula assumes unity power factor for a resistive heater load.
Assumptions
- The estimate treats the heater as a unity power-factor resistive load.
- Voltage is nominal and must match the heater nameplate and supply system.
- Multi-step heaters, controls, manufacturer data, and nameplate current can change the practical current used for review.
- This calculator does not size heater branch circuits, conductors, overcurrent protection, disconnects, controls, or HVAC safety devices.
Examples
5 kW at 240 V. A 5 kW resistive heater at 240 V single-phase estimates about 20.8 A.
30 kW at 600 V. A 30 kW balanced three-phase heater at 600 V estimates about 28.9 A before nameplate and branch-circuit review.