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What Size Breaker for 4000 Watt Heater? – A Detailed Answer

Written by Edwin Jones / Fact checked by Andrew Wright

What size wire do I need for 4000 watt heater

Do you know what size breaker for 4000 watt heater you should use? Did you know how important it is to have the proper breaker capacity for your appliances and equipment?

The appropriate circuit breaker capacity for a 4000-watt heater is 20 amps if it’s attached to a 240-volt outlet. If you use a lower-amp breaker for this heater, it will cause the electrical system to overload and the breaker to trip. That’s why it is crucial to consider the capacity of your breaker before installing any heavy-duty device.

Read on to find out more about ideal circuit breaker capacities.

Why Do I Need a 20-amp Circuit Breaker for My 4000 Watt Heater


To know the appropriate amp capacity for any machine, you have to do a little math. In school, you will learn that Watts = Amps x Voltage. So, if you have a 4000-watt heater and a 240-volt source, you can compute the amp requirement.

To do so, divide watts by voltage to get the amps you need. 4000 divided by 240 is 16.6 amps. Since you can only pick between 15-amp and 20-amp circuit breakers, you should choose the bigger one.

You can refer to this video by S33 Electrical, which shows the proper computation using the above formula. Although it is not the same example as above, the fundamental theories remain the same. You can use the above procedure to compute the amp capacity required by any device or machine in your home.

One more thing—the 16.6 amp requirement of a 4000-watt heater is the bare minimum. This is because you should only use up to 80% of a circuit breaker’s capacity continuously. So, a 20-amp circuit breaker has an ideal continuous load capacity of 16 amps.

So, if you plug another device with more amps into the same circuit your heater is using, it may cause the breaker to trip due to overloading. Furthermore, if it doesn’t overload immediately, it will slowly heat your heater’s wiring, eventually causing the breaker to trip.

If you want to install a more powerful heater, you should consider upgrading your circuit breaker and ensuring that the wires installed in your walls are capable of handling the added capacity. Also, avoid plugging additional electronics into the circuit of the heater.

What if You Have a Less Powerful 110V Heater

Using the same formula above, divide the required device watt consumption by your voltage requirement. For example, if you have a 2000-watt heater that uses 110-volt power, its amp requirement is 18.18 amps.

If you consider the 80% suggested limit of most breakers, you will have to use a higher capacity 25A breaker.


Most appliances, devices, and electronics indicate how many amps they require. And even if it’s not noted on the machine or in its manual, you would usually find its wattage indication. Furthermore, you must know what breakers your devices need to prevent damage in your house.

Now that you know what size breaker for 4000 watt heater you should use, you can now get a suitable capacity breaker for other water heaters, such as  10,000-watt heaters and 4500 watt water heaters. So, did I help you with your problem through this article? Do you have additional questions in your mind? Don’t be afraid to share them in the comments below!

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