How To Bypass The Thermostat On An Attic Fan

Although an attic fan helps to keep your house cool in the summer, you might sometimes wonder whether the extra electricity that the fan uses, and thus, the money it costs you is worthwhile. Perhaps you’ve wondered whether you can bypass the thermostat and just put on the fan manually when needed. 

Yes, you can bypass the thermostat on an attic fan. And it is relatively simple to do. You only have to follow a few basic steps and it is done. You can even wire it in such a way that you can switch between the default (working with a thermostat) and a manual operation with an on/off switch.   

In this article, we’ll discuss the wiring to bypass the thermostat, and we’ll look at some of the reasons why people want to bypass the thermostat. We’ll also answer the question of why people install an attic fan in the first place. 

How to bypass the thermostat

If the attic fan’s motor, the thermostat and an on/off switch are connected in a specific way, you will be able to bypass the thermostat. And it is quite easy to do the wiring to achieve this. Generally, you just have to follow the following steps:

  • Step 1: Install a 12-3 wire from the switch box to the fan thermostat box. 
  • Step 2: Use one of your wires to take power directly to your thermostat. It can be either the red or the black wire. 
  • Step 3: Run the other wire from your switch to your fan.  Splice it in with the wire already going from the thermostat to the fan motor. In other words, you wire the system in such a way that the power from the switch can go straight to the fan motor. 
attic fan thermostat

The result is that when the switch is off, you are still providing direct power to the thermostat that is controlling the fan. But when you turn the switch on, it bypasses the thermostat and gives the fan motor power directly. Thus, you’ll always have two choices. You can let the thermostat control the attic fan by leaving the switch off, or you can manually bypass the thermostat by putting the switch on. 

Why do you want to bypass the thermostat?

The most important reason why people want to be able to bypass or override the thermostat on an attic fan is to prevent the fan’s motor to burn out. 

Over time an attic fan’s outlet can get blocked. If the fan’s outlet is blocked completely it can prevent the motor from running. This might cause the fan’s motor to burn out. 

So, when you detect that your attic fan is not working properly, you want to be in a position to stop the fan from working without switching off your whole HVAC system or the AC. Switching off the attic fan manually can prevent burnout. 

You’ll also want to be able to turn off the power to your attic fan while the rest of your HVAC system is still working when you for any reason, want to work on the fan or the motor. You, for instance, want it off when you clean the outlet and blades, remove dust build-up, or just do normal maintenance on the motor. 

Why do you need an attic fan in the first place?

There are several reasons why it is good to have an attic fan installed in your home. Especially in the summer, an attic fan can be of great value to the temperature regulating processes in your home.  

If your home doesn’t have an attic fan, you most probably cannot go into your attic on a summer day to fetch something that you’ve stored there because of the heat in the attic. As there is no fan to extract the hot air, temperatures in the attic can rise to 145 degrees Fahrenheit and more. That heat can also get into the rest of your house if the insulation is either old or not sufficient. 

A properly installed attic fan can remove most of the excessive heat build-up in the house and provide you with a cool attic space. It reduces the pressure on your insulation systems and prevents unwanted heat to transfer into your living space.

One important benefit of having a working attic fan in your home is that the AC doesn’t have to work 24/7 to keep your house cool in summer. With the excessive heat removed by the attic fan, the AC doesn’t work so hard. AC maintenance cost is also lower and less power is used. (If you then also can manually switch off your attic fan when it is not really needed, you can even save more electricity and money.)


It is always good to know how to bypass your attic fan, and if you are not a DIY person it is good to know that it is possible that an attic can be wired in such a way that the thermostat is bypassed – then you can ask your electrician to do it for you! 

As discussed above it is good to have an attic fan as part of your HVAC system in your house, but you can save money and power if you have the choice to manually put off the fan when it is not needed.

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Charles John

Experienced HVAC technician with 8 years of experience in the industry. Capable of handling all sorts of heating and cooling equipment as well as proficient in operational management, construction-related techniques such as preventative maintenance, electrical troubleshooting and AutoCAD

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