How to Wire an Exhaust Fan to a Thermostat

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Wiring a thermostat to an exhaust fan allows the fan to operate based on temperature. This set-up is especially useful in greenhouses. The thermostat used in this instance, though, isn't your typical thermostat. It's a reverse thermostat, which works by turning on the exhaust fan at a certain temperature then turning it off after the temperature has cooled adequately. These thermostats are usually line voltage, which makes them fairly easy to wire to an exhaust fan.

Things You'll Need

  • Tape measure
  • Screwdriver
  • Hammer
  • Electrical box
  • Electrical wire
  • Drywall saw
  • Wire stripper
  • Wire nuts
  • Line voltage reverse thermostat

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Turn off all power to the exhaust fan. This is accomplished by turning the correct breaker off in the circuit breaker panel.

Mount an electrical box where you want the thermostat control to be located. You may need to open up drywall to mount the box to the studs in the wall.

Check the amperage draw of the exhaust fan and run a suitable wire size from the switch box to the exhaust fan. The wire should have two conductors (black and white) and a ground (green). If it's 15 amps or under, you'll need 14 gauge wire; if it's between 16 and 20 amps, you'll need 12 gauge wire.

Connect the wires to the fan (black to black, white to white, and green to green). Use wire nuts to make all connections.

Remove the thermostat cover to gain access to the wiring. Connect the black wire coming from the exhaust fan to the red wire on the thermostat. Connect the white wire coming from the exhaust fan to the black wire on the thermostat. Use wire nuts to make these connections. Connect the ground wire (green) to the terminal screw in the electrical box.

Fasten the thermostat body to the electrical box and push the cover back on.

Patch any drywall if necessary and turn the power back on to the electrical circuit.


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