How Many Amps Does a Water Heater Use?
A 4500W electric water heater at 240V draws 18.75 amps.
Water Heater Amps Explained
The standard heating element size for a residential electric water heater in the US is 4500W at 240V, which draws 18.75 amps. Per NEC 422.13, water heaters are treated as a continuous load, so the branch circuit must be rated for at least 125% of that current. Depending on the specific unit's nameplate rating and local code, this typically works out to a dedicated 25A or 30A breaker with 10 AWG copper wire. Always check the nameplate rating on your specific unit rather than assuming 4500W, since some water heaters use 3800W or 5500W elements.
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.