Adding a humidity switch for an exhaust fan

It’s not practical and efficient to run the bathroom exhaust fan every time there isn’t the need for that. There is an easy and good way to save money. You can buy a secondary swith that will turn on the fan only when it’s needed.

Tools and materials that you’ll need:

  • electrical tape
  • Phillips screwdriver
  • flat screwdriver
  • ladder
  • drywall saw
  • flashlight
  • 2 feet of 14-2 romex
  • 3 wire nuts


Step1. Ceiling opening

You need to cut an opening in the ceiling or wall, big enough for the fan to fit. The size should be 1.75 inches across by 3.5 inches up and down. The sides of the opening should be at about 1 inch from the fan cover.

Step2. Mounting

Open 2 of the wire entry points on the back of the box. You can now mount the box next to the exhaust fan.

Step3. power supply

Open the cover of the junction box that supplies power to the fan. Disconnect the supply wire from the fan. Route supply wires into the box you have mounted. Route the romex you bought between the 2 boxes.

Step4. Reconnect

Connect the fan wires to the romex. Replace the cover.

Step5. Connection

Insert the other end of the romex into the new box. Make connections between the supp;y wires of the fan and the switch. You may need to use screw terminals or nuts.

Step6. Finishing up

It’s much easier to install the humidity switch next to the primary switch, than installing it next to the fan. But, as vapors rise up in the bathroom, it’s more effective to put the switch next to the fan.

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