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Bathroom Exhaust Fan and Light Electrical Wiring

By Dave Rongey - Summary:

How to Wire a Switch for Bath Exhaust Fan and Light: I have a new bathroom exhaust fan heater light to install in place of an old one and wire the switches.

Switch Wiring for Bath Fan and Light

Electrical Question: I have a new bathroom exhaust fan heater light to install in place of an old one and wire the switches.

  • I also had a fan heater light. The new fan is a Nutone QTXN110HL.
  • The Wall switch box and wiring are already installed and worked with old fan.
  • The wires are by the fan – red, yellow, black, blue.
    Two sets of wires come from fan (1) for heat and nightlight (2) for light and fan.
  • One group of wires is red, white, blue? The other is Black, white, yellow.
  • I assume the ground wire is attached already somewhere ?¬† I don’t know which wire¬† is which, except that black and red are hot for light or fan motor. Heater? yellow for nightlight?
  • The wiring diagram and pic that came with the unit make absolutely no sense and there are no written instructions for the wiring part. Any idea which wires go where?

This electrical wiring question came from: James , a Homeowner from Laramie, Wyoming.

Additional Comments: I like the website. Lots of useful and helpful information for a guy with limited knowledge about these things :)

Dave’s Reply:
Thanks for your electrical wiring question James.

How to Wire a Switch for Bath Exhaust Fan and Light


wiring a bath exhaust fan and light

Application: Wiring a Switch for a Bathroom Exhaust Fan and Light.
Skill Level: Intermediate to Advanced, best installed by a licensed electrical contractor.
Tools Required: Basic Electricians Pouch Hand Tools and a Voltage Tester.
Estimated Time: Depends on personal level experience, ability to work with tools and the access to the wiring for the wall switch for the exhaust fan and if a larger switch box will be required.
Precaution: The combo bathroom exhaust fan circuit should be identified, turned OFF and Tagged with a Note before working with the wiring and installing the fan speed switch.
Notice: Modifying existing wiring or installing additional bathroom electrical wiring should be done according to local and national electrical codes with a permit and be inspected.

How to Wire Switches for an Exhaust Fan


  • The Power Source
    There is one power source that is shared with both switches.
  • Fan and Light Switches
    You will be using multiple switches for individual functions.
  • Wiring the Switches
    Each switch function requires the appropriate wire color.
  • White Neutral Wires
    The neutral wires are spliced together.

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4 Responses to “Bathroom Exhaust Fan and Light Electrical Wiring”
  1. mike says:

    I have an existing bathroom fan{only}I took it out to clean but now i cant figure out how to wire it back up ..no ground on the power side just black and white same on the fan and wire going to the switch,when i put the 3 black wires together and then the white ones the fan always runs what am i missing? Thank you.

    • Dave Rongey says:

      Hi Mike,
      From what you have described, one set of black and white wires are most likely the wires used for switching. To fix this problem both sets of wires need to be identified as the incoming power, and the switched wires. The black wire of the incoming power is then connected to the other wires which will got down to the switch and back up. Connect the wiring accordingly. The white neutral of the power source connects directly to the white neutral wire of the bathroom fan. Keep in mind that the wires used for the switch just creates a loop where the switch is in the middle.
      I hope this helps,

  2. Pat Beck says:

    I have 2 switches to control my light and bathroom fan. The light is the red feed.
    The new fixture, fan/light combo, has a capacitor red from motor-cap; capacitor out is black to white at motor
    also from motor is a white to light & black to black light

    How do I connect my w/b/red from my switches?

    • Dave Rongey says:

      Hi Pat,
      Quite honestly I would look at the wiring diagram that came with the new unit. I rarely have seen a bathroom exhaust fan with a cap, and if so they are pre-wired or connected where the only leads left were the 120 volt line connections.


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