How Many Amps Does a Space Heater Use?
A 1500-watt space heater uses 12.50 amps at 120V. It requires a dedicated 20A circuit per NEC 210.20.
Space Heater Amps Explained
A standard 1500-watt space heater draws 12.50 amps at 120V AC. Because a space heater runs continuously for extended periods, it qualifies as a continuous load under NEC Article 210.20, requiring a dedicated 20A branch circuit. Never share a space heater circuit with other high-draw appliances.
Frequently Asked Questions
How do I convert watts to amps?
For DC circuits, divide watts by volts (Amps = Watts ÷ Volts). For AC single-phase circuits, divide watts by the product of power factor and volts. For AC three-phase circuits, divide watts by the product of √3, power factor, and volts.
Why do I need power factor for AC calculations?
Power factor accounts for the phase difference between voltage and current caused by inductive loads like motors and compressors. Purely resistive loads (heaters, incandescent bulbs) have a power factor of 1.0. Motors typically run 0.8–0.95.
What breaker size do I need for a 1500W appliance at 120V?
1500W at 120V draws 12.50 amps. Per NEC Article 210.20, continuous loads must not exceed 80% of a breaker rated capacity, so a 15A breaker (12A max continuous) is not sufficient. A dedicated 20A circuit is required.
Does this calculator work for 240V appliances?
Yes. Enter your wattage and set voltage to 240V for dryers, water heaters, ranges, and EV chargers. At the same wattage, 240V circuits draw half the current of 120V circuits.
Is this calculator accurate for 3-phase industrial power?
Yes. Select the AC 3-Phase tab, enter your line voltage (commonly 208V or 480V), and choose line-to-line or line-to-neutral mode. The calculator uses the precise value of √3, not a rounded 1.732 approximation.
Can I use this to size wire gauge?
The calculator provides an AWG wire gauge recommendation based on NEC Table 310.15(B)(16) for 60°C copper conductors. Always confirm final wire and breaker sizing with a licensed electrician before installation.