Two Breakers In My Furnace: Why Is That?

Last Updated on May 14, 2025 by Chad Peterson

Electric furnaces often have two breakers because the furnace requires a larger amount of power, which exceeds the capacity of a single breaker. Here’s why:

Breakers are an important safety feature of air handlers or furnaces. Circuit breakers are not just a switch to turn a furnace on and off. They protect the wire that feeds the power to your furnace in case of an overload such as a shorted motor or heating element.

The amount of current or electricity that a furnace uses is a “load” on the circuit or wire that feeds the furnace. If the load is large enough it makes sense to divide that load into two or more circuits using a breaker for each circuit.

DISCLAIMER: This is not a guide. This article is about why furnaces have two breakers. Wire sizes can vary by local codes, wire length, type of wire, and temperature. The wire sizes mentioned here are for explanation purposes only.

A larger load requires a larger wire. Copper wire can be expensive and depending on several extenuating circumstances from both the manufacturer to the installer, a decision has to be made as to the number of circuits and the wire size.

Most electric furnaces or air handlers in my area have two breakers, the most common load being 15KW. One breaker being a 30 amp which takes care of 5KW and the other a 60 amp which takes care of the remaining 10KW. The combination of the two creates a 15KW furnace.

For most installations of a reasonable length a 30 amp breaker can be fed with number 10 copper wire and a 60 amp breaker with a number 4 copper wire. Using aluminum wire is a whole other story not discussed here.

What If There Are Two Breakers In My Furnace And Only One In My Panel?

Sounds confusing maybe but it’s a real thing. You’re looking frantically for the second breaker in your panel to shut of the air handler but all you can find is one. It’s a single conductor or wire in a main electrical panel that is feeding two breakers in a furnace.

If you are confident, willing, and able to look inside your furnaces control panel your would see what is called a single point connection. Similar to the one pictured below.

Which by the way is a link to this product on Amazon in case you have a need for one or simply want to know about what they cost. In my opinion they are way too much for what they are.

Single point connectors allow a single conductor (two hot leads and a ground wire) to be run from the main panel to the air handler. Looking at the image above, notice the two lugs at the bottom.

The wire from the panel connects to these lugs and then the red and black wires on top connect to the two breakers in your furnace. Essentially they are split or divided in two to feed two breakers. The image below shows a single point demand wiring kit installed in a furnace.

Who knows what the price of copper has to be to decide to run a single conductor to a two breaker furnace. That’s about 90 amps for the example given earlier of 15KW. The 30 amp and the 60 amp breakers.

That’s getting into some heavy copper wire, somewhere in the area of keep your doors locked or copper thieves will find you and strip the wire out of your walls. Don’t get paranoid.

Another example of how one conductor can feed two breakers. Notice how the conductors on the right connect to the breakers. The wire on the right connects to each breaker on the top. The wire on the left connects to each breaker on the bottom feeding 240 volts to each breaker.

What Is A Piggyback Breaker?

Could be called a tandem breaker. Not likely to be found inside a furnace or air handler. It’s used to make room in a main power panel. Piggyback breakers have several names like twin or slim or wafer. Sometimes a panel can fill up fast, especially after years of remodel and additions.

It’s customary and even allowable under certain conditions to wafer up a panel to allow more circuits. Overloading the panel is one of those certain conditions. Only your electrician knows. Well, maybe you do also.

Keep in mind that there are generally two types of breakers in a panel. Not speaking of brands, but sizes. Sizes in relation to voltage. There are single circuit breakers that feed your lights and receptacles (the plugins on the wall).

And there are double circuits, they are the wider switches. If you look close you can notice that the switch or toggle on a double breaker connects to what sort of looks like two single breakers.

Double breakers feed appliances like your air conditioner, electric range, dryer, electric water heater, etc.

I hope you feel that this is all good to know stuff. I have a lot of customers who have no clue and this is important to your safety and the serviceability of your home.

You need to know what circuit breaker go to what circuits or appliances. It’s always a little too late when you need to shut off an appliance and you can’t determine which breaker is the right one to switch and make the kill.

Conclusion

Knowledge is power.