This article explains the different methods to cut power to a thermostat when replacing or removing it.

When you want to turn off the power supply to your HVAC thermostat for whatever reason, you might suddenly realize that you don’t know where and how to do it. You don’t even know whether it is necessary to turn off the power to the thermostat for what you want to do. 

There are different ways to turn off power to your thermostat and it is always good practice to cut the power to the thermostat if you want to work on the HVAG system or suspect any malfunctioning in the system. Your HVAG system and how it has been installed will dictate to a great extent how and where to turn off the power to the thermostat.  

You have more than one option of how to turn off the power to your thermostat. Let’s look at some of these options. The options are not discussed in any priority – you can decide which method will suit your circumstances the best. 

Shut down the whole HVAC system – with one circuit breaker

In most households, the HVAC system is using only one circuit breaker for all the applicable appliances in the house. If this is the case with your system, it is easy to turn off the power to the thermostat. You just put off the circuit breaker marked “HVAC,” “Cooling” or “Heating.”  All power to the HVAC system will be cut. This means the power of the thermostat will also be turned off automatically.

However, you might encounter a problem with the breaker panel if the breakers are not marked. Without indications on the panel of which appliances are serviced by which breaker you will not be able to determine which breaker is controlling the HVAC system by just looking at the panel. The only way then to determine which breaker is the correct one, is to put all your HVAC appliances on and by turning the breakers off one after the other determine which breaker control your HVAC system.

Shut down the whole HVAC system – with more than one breaker 

Sometimes the appliances that form part of your HVAC system use different circuit breakers. Normally you will not know from which appliance your thermostat is receiving its power. It most probably will be the furnace or the AC. Thus, to ensure that the power to your thermostat is definitely turned off, you’ll have to put off all the corresponding circuit breakers.

If the breakers are marked, put off all breakers referring to HVAC-related appliances. You might, however, encounter the same problem at the breaker panel as described above if the breakers are not marked.  Then you have to follow the same procedure and put the breakers off one after the other to find the applicable ones to be off. 

Shut down all the power in your house

If your breaker box isn’t labeled, and you can’t determine when your HVAC system is off, you can switch off the main breaker. This will shut down all the power in your home. But it is important to remember that doing this affects all other electronics in your home. After you’ve turned the power back on, you might have to reset things like the time on clocks.

Cut the power to your AC and furnace only

Usually, the small, low-voltage transformer supplying power to the thermostat can be found in or near the AC/heating unit.  But sometimes it is installed in or near the furnace or even on the breaker panel. Find the thermostat and turn the power to that appliance off, or put off the switch if it is located on the breaker panel. Disconnecting or turning off power to the AC and/or furnace will automatically cut power to the thermostat if it is embedded there. 

You can turn the power off to these appliances by putting off the breakers as described earlier in this article, or turn off the power on your AC and furnace by simply flipping off the power switch on the units themselves.

You just have to remember that there are usually at least two transformers in a home. The one is for the doorbell and the other one for the thermostat. Ensure that you cut the power to the right transformer. If you’re not sure which one is which, put the power off to both!


There are different ways to put off the power to the thermostat. You can use any of the methods discussed in this article. Although most room thermostats operate on low voltage and thus carry little risk of electric shock, it is always good and safe to shut off power to a thermostat before working on it.


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