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What Size Breaker Do I Need for a 4500 Watt Water Heater?

Written by Edwin Jones / Fact checked by Andrew Wright

what size breaker do i need for a 4500 watt water heater

To answer the common homeowner query, “What size breaker do I need for a 4500 watt water heater?”, you’ll need either a 25-amp or 30-amp circuit breaker. This answer is in accordance with the 125% rule set by the National Electric Code for circuit breakers, which requires using the breaker for no more than 80% of its rated current for continuous loads.

Are you curious about how to arrive at this answer? Read on to know how you can calculate it, too. Also, I’ve made it clear once and for all why there are some cases when CBs are fine to size at 100%, while there are others when this isn’t applicable.

How to Calculate the Correct 4500-Watt Water Heater Breaker Size

The breaker size has always been calculated by dividing the total wattage by voltage. So to know what size breaker for a 4500-watt water heater, we need to divide 4,500 by 240. The answer to this is the exact figure you get when you convert 4500 watts to amps: 18.75.

Since a water heater is a continuous load device, we need to multiply that value further by 125%. The result is 23.4 amps. The right circuit breaker for this appliance with 4500 watts at 240 volts is either 25 amps or 30 amps.

If the water heater isn’t rated as “continuous load”, then it would have been fine to use 100% of the circuit breaker’s rating. As far as circuit breakers go, it’s either 80% for continuous loads or 100% for noncontinuous loads.

If you have the time, please watch this video that expounds on various other calculations related to using the proper circuit breaker size for any kind of application:

Remember: It’s important to know whether your device is a continuous load or not, especially if you don’t want your breaker to trip constantly. Using the wrong size ups the risk of short circuits as well!

Don’t Forget About the Right Wire Size, Too!

The appropriate breaker and wiring size always go together, after all. The correct 4500-watt water heater wire size is a 10/2 wire or a 10-gauge non-metallic wire. If you already know it, we hope this information about what size breaker do I need for a 4500 watt water heater confirms it for you. If you own other water heaters, click here to find out about the right size breaker for a 4000-watt heater and a 10,000-watt heater.


To sum it up, you can either use a 25-amp or 30-amp breaker for a 4,500-watt heater. For wiring, you can choose between a 10-gauge wire or a 10/2 wire for this setup.

Now that you know the right breaker size and wire gauge for a 4500-watt electric hot water heater, we hope you won’t stop educating yourself about correctly handling your own electrical systems. Even an ounce of know-how can make the difference in ensuring you do it properly and safely.

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