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What Size Breaker for a Hot Water Heater?

Writen by Ronald Brown

Fact checked by Natalie Bridges

What Size Breaker For A Hot Water Heater

Do you have an electric water heater at home? You might want to acquire information about what size breaker for a hot water heater you should use. This requirement is critical because the circuit breaker protects the electrical system of your water heater.

Most electric heaters need a 240-volt dedicated circuit; This circuit includes a 30-amp two-pole breaker with a 10-2 non-metallic cable or metal-clad cable. A perfect breaker size should be proportionate to the electrical specifications of your water heater.

Table of Contents

How Does A Circuit Breaker Work?


An electric breaker or most commonly known as a circuit breaker, is in charge of maintaining the safety mode of electrical connections, especially if there are short circuits or overcurrent events.

It interrupts the current flow to avoid circuit damages that can cause fires and overall electrical system failure. It acts as a safety device to prevent any electric shock or disruptions to your water heater’s operation.

How To Find The Proper Breaker Size For Water Heater?


When talking about the actual breaker size you need for your water heater, it is important to consider your circuit’s capability. The question you should ask yourself is “What maximum electric current do I want to pass through the circuit?”

According to the National Electrical Code, the circuit breaker size should not be lower or higher than 125%. To find the appropriate breaker size, we must follow these four easy steps. At the end of this discussion, you should be able to select a circuit breaker for your water heater.

  • Determine the water heater power rating

The first thing you should do is to determine the current rating of your water heater. You can find this information in the specification label found on the side of your heater. Typically, residential water heaters consist of 1500 watts energy rating.

If your heater operates on a 240-volt capacity, it uses 4,500 watts. If a water heater contains two heating elements, you will notice two wattage values – but they don’t run simultaneously.

A water heater with two elements that indicate a 4,500-watt energy rating for each uses a maximum amount of 4,500 watts. You don’t necessarily add the two wattages.

You can check out this guide to choose the right watts for your water heater.

  • Calculate the maximum current of your water heater

Identifying the maximum current of your water heater is imperative because it will help you find a breaker that matches its overall operating system. The formula is quick and easy. Divide the power rating of your heater by the operating voltage.

If your electric water heater runs at 1,500 watts with a 120-voltage connection, then you would have to divide these two variables. Therefore, you’ll get 12.5 amperes in total.

  • Check the ideal amperage for your water heater

Why is it important to check the correct operative amperage? It is because there are cases where the breaker size may not be congruent with your heater’s operating voltage. For example, a 1500-watt heater with a 120-volt circuit should have at least 15.6 amps.

However, a 15 amp breaker might be a little undersized for this setup. Hence, you would need a breaker with a higher rating. A 20-amp breaker perhaps would most likely be the best option.

  • Calculate the current rating of your continuous and non-continuous load breaker

This step will finally tell you what breaker size you should avail. Multiply the value of the current rating by 125%. Homeowners often assume that the maximum amp of their water heater indicates the same amount of breaker amperage.

The general rule of thumb is to get a higher rating of circuit breakers since each of them can only use 80 % of their overall amperage. For instance, a 15-amp breaker can only take 12 amps, while a 20-amp breaker can take up to 16 amps.

Generally, Circuit breakers and Overcurrent Protection Devices are designed to handle 100 % rated current. In this case, you can use a smaller breaker, most specifically on the subject of non-continuous load. But for continuous loads, the 125% recommendation is advised to obtain a safe current limit.

Hence, the case in no. 3 is also applicable here. It is essential to determine the load capacity of a circuit breaker. We must ensure that our water heater is compatible with the breaker we choose.

Example 1: Find out the circuit breaker size for a 30A non-continuous load water heater

You may use a 30 amp circuit breaker for 30A non-continuous load. An exact 100 % current rating is appropriate here.

Therefore, 30A non-continuous load = 30A breaker. No further adjustment and computation are needed.

Example 2: Find out the circuit breaker size for a 28A continuous load water heater

In this problem, we need to multiply the 28A continuous load by 125% as supervised by NEC.

1.25 x 28 A = 35 A

Hence, the breaker size equals 125 % of the continuous load.

Points To Remember When Choosing A Circuit Breaker Size

  • The 125% calculation only applies to continuous loads. Most water heaters that operate in 240 voltage circuits can use it.
  • If you’re going to use your water heater intermittently (non-continuous), a 100% rated circuit breaker is good to go.
  • A 30 amp breaker needs a 10 gauge wire size. Both devices can be used in 240V heaters.
  • If other devices are linked with the same circuit as your water heater, add their amperage to the total current draw.
  • If you reduce the breaker size without replacing the overall wiring and circuit, the safety feature of your breaker disappears.
  • A circuit breaker would trip and break easily with bad wiring.
  • A faulty thermostat can make your breaker draw out more power which eventually leads to tripping.
  • Breakers can’t be larger than the ampacity of the wire unless the load current is high.
  • It is advisable to use a circuit breaker twice the amount of your water heater’s amperage.
  • Always make sure that the circuit breaker is compatible with the existing panel.


Choosing the exact breaker measurement is tricky. When consolidating information about what size breaker for a hot water heater you must use, always look for the specification sheet of your water heater. You will use it as a basis for your circuit breaker size computation.

By following the steps above, you can decide what kind would work accurately with your water heater. This action plan should not be taken for granted, as it ensures that your water heater won’t encounter any electrical issues.

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