【How-to】How many amps does a 4500 watt water heater draw

For a 40-gallon heater, the average capacity is 4500 Watts with 240 Volts. Again, I = P/V; 4500W/240V = 18.75 amps. Then considering the continuous load (125% x 18.75A), we’ll get a total of 23.4 amps. With our answer, a 40-gallon water heater needs at least a 25-amp breaker, the closest to the amperage value.