Which Breaker In My Panel Goes To My Furnace?

Many of the service calls I go on have electrical panels in which the breakers are not labeled. This takes extra time and adds cost to a service call. Make sure that when you find what breaker goes to whatever appliance or circuit that you mark them clearly.

This is an easy process of elimination. Go to your thermostat and turn the fan switch to the “on” position so you can hear the fan running. If you have no fan switch then turn on the furnace. Get back to the electric panel and start to turn off and then on again, one breaker at a time.

If your furnace is in another room from your panel it’s best done with a helper. Connect yourselves with your cell phones if necessary. Wait for your helper to respond that the fan has shut off before turning each consecutive breaker back on again before turning off the next.

Before you do this it’s important to understand some simple instructions regarding breakers that will help you do this whole process a little faster.

Two Pole Vs Single Pole Breakers

A gas or oil furnace (fossil fuel furnaces) will be powered by a single breaker feeding 120 volts to the furnace. Electric furnaces will have two pole breakers. You need only check the single lever breakers that supply 120 volts to your home circuits.

The double lever breakers that are marked 240V below feed those appliances in your home like your range, clothes dryer, electric water heater, etc. So if your heat source is fossil fuel you need only check that single levered breakers that look like the ones marked 120V.

The breakers above are full sized breakers. You may see some that are thinner in your panel. These are called slimline or tandem breakers. I’ve heard them called thins or even wafer breakers.

These thin breakers are used to make more room in a panel for additional circuits.

An electric furnace will be fed by one or more double breakers feeding one or more circuits of 240 volts. This can get a little tricky because of how the original electrician may have wired your heating equipment.

So when looking for the breakers for an electric furnace, only trip the double 240V breakers. It’s possible to turn a breaker off that stops an electric furnace and still have power to the furnace by a second breaker.

A really handy tool that I use often is a Fluke non-contact voltage checker. that you can purchase on Amazon. You just touch it to a wire on the insulated covering and it alerts you that the wire is hot. Never completely trust a tool such as this. Always double test. Treat wires like they are hot just like you treat all guns as if they are loaded.

With one of these little critters you can take the cover off the furnace and turn off breakers until the tester doesn’t light up.

One breaker in a panel could feed two breakers in a furnace with what’s called a single point connector. I explained this more thoroughly in an article titled Can I Install Any Brand Furnace In My Manufactured Home?

The wiring diagram for a single point connection would look like this……………..

Don’t turn a heat pump or an air conditioner off and on because they should not be short cycled even though they should have delays built into the units or even in the thermostat. The delays will only confuse you when you turn the breaker on and off.

If the outdoor unit is the breaker you’re looking for, go ahead and turn it on at the thermostat and then when your helper says it’s off when you trip the right breaker, then wait 5 minutes before resetting the thermostat, just in case.

Some furnaces are in the same room as the main power panel of circuit breakers and having a helper in unnecessary. Be careful to turn off any computers or equipment that shouldn’t be turned of and on abruptly.

Are Some Circuit Breakers Dangerous?

I know that whenever I come across Zinsco and Federal Pacific Electric I like to inform my customers of the possible dangers of these breakers. You may see the name Stab-Loc on the side of the FPE breakers.

I’m not a licensed electrician. I carry two electrical licenses for the state of Oregon. One allows me to work on electrical components inside of HVAC equipment and up to a disconnect. The other really crazy one allows me to pull thermostat wire.

In some areas of the country the licensing is different. HVAC service technicians are allowed to run circuits from electrical panels to there new equipment. All of this gives a technician quite a bit of experience in troubleshooting and diagnosing bad circuit breakers.

If your panel is one of these it would be a good idea to have an electrician service your panel to make sure it’s safe.