What Size Breaker Do I Need for a Furnace?

Image of electric furnace source Provincial Heating

After buying a furnace and preparing to install it, the next thing that you need to think of is buying the right circuit breaker. Which is the perfect breaker size for a furnace? In all cases, it will always depend on the electrical load of the furnace. The right breaker size for the furnace is between 80 to 100 amps.

From this range, you can tell that there is no fixed breaker size for the furnace. There are many variables that will determine the right breaker size that you should use.

Keep reading as we break down the actual numbers of the circuit breakers with regard to the furnace.

Table of Contents

80% rule for continuous load

How have we arrived at the 80 amps to 100 amps figures for the circuit breaker size? One of the key factors that we have considered is the 80% rule for the continuous load. We can define a continuous load as any electrical load that is designed and expected to run continuously for up to more than 3 hours. Heating appliances such as heaters, air conditioners, and furnaces belong to this category.

The 80% rule states that the maximum load on the electric circuits that are connected to these appliances should not be more than the 80% capacity of the circuit. Let’s say if the circuit is designed to have a capacity of 100 amps, the maximum load circuit at any given time should not be more than 80 amps.

The 80% continuous rule is there to guarantee the safety and efficiency of the circuit. It prevents incidences of current surges, overheating, and even electrical damage to the circuit components.

So, when choosing a circuit breaker for the furnace, you should always remember this 80% rule since the load will run continuously.

Calculate the amp capacity of the circuit

Back to the facts and figures. We have to do some calculations to get the approximate circuit breaker size for the furnace.

The first thing that you will have to consider in the calculation is the supply voltage. In most households, it is either 220V or 240V. The next thing to consider is the watt rating of the furnace.

To get the amp capacity, you will simply divide the watt rating by the supply voltage.

Let’s say your furnace is rated 20,000 watts and you will have to connect it to the 240 volts power source.

The amperage for this furnace will be 20,000/240 volts which will be 83 amps.

Now bring in the 80% rule you will end up with almost 100 amps circuit breaker.

This formula of watt/voltage works on all the electrical appliances not excluding the furnace. Whether you have a larger or a smaller furnace, you should be able to use it to get the actual breaker size.

How will I know the watts for the furnace?

As we have mentioned, watts are a critical component for helping find the right breaker size. The wattage is usually labeled or indicated on the surface of the furnace or on its packaging.

Check the nameplate which is basically a piece of metal attached to the furnace. It will have the model number, serial number, and all other electrical specifications of the furnace.

The value is usually indicated in watts (W) and sometimes kilowatts (kW). So do the necessary calculations and use the figures.

Does the furnace need to be on its own breaker?

Image of circuit breaker source Freepiks

Yes, you will need a dedicated breaker on each furnace. This is in line with the building codes which require that a furnace should be served by a dedicated circuit. Since each circuit in the building is connected to a circuit breaker, you will have no other option but to use a single breaker for each electric furnace.

What if I have more than one furnace in the building? The rules still remain, each one of them will have a dedicated circuit, and subsequently a dedicated breaker.

As we have seen from the specs, furnaces are power-hungry appliances. They require high amounts of currents to keep running making it difficult for them to share circuit breakers.

What is the recommended wire size for the furnace circuit?

Other than the size of the circuit breaker, you should also pay attention to the size of the wire.

2 AWG is the perfect size for most circuits that are connected to furnaces. It is big enough to accommodate the high current needs of the furnace.

Are circuit breakers for furnaces expensive to replace?

From this guide, one of the recommended options is replacing the circuit breakers for the furnace. What does it cost to replace a breaker and are they expensive?

Circuit breakers for the dedicated furnace circuits are just like ordinary breakers. This means that you will not pay any extraordinary price for each. The cost may vary depending on the amp capacity of the circuit breaker.

Also, the brand of the circuit breaker will always matter. Some brands are cheap while others are quite pricey. Not forgetting that the suppliers and distributors have an influence on the final price of the circuit breaker.

Take your time to know more about the manufacturers, suppliers, and distributors of circuit breakers for furnaces if you want to get the best deals. Of course, buying circuit breakers wholesale is just one of the tricks for getting them at the right prices.

Conclusion

There are various safety precautions that you should take when buying and installing an electric furnace. One of them is choosing the right circuit breaker size. You will have peace of mind knowing that the circuit breaker will protect the furnace and its circuit from any hazards related to current overload, and short circuits, among others.

And there is more to it than just the size of the circuit breaker. It should be of high quality. Low-quality circuit breakers are easily compromised when connected to high-current loads such as furnaces. Choose a reputable circuit breaker supplier if you want to be sure of the quality factor.

The same rule applies even when you are in the business of buying circuit breakers in bulk for resale. Don’t compromise on the quality factor as it may end up leaving a dent in your reputation.