How do I wire a bathroom exhaust fan and light on separate switches?

Wiring a bathroom exhaust fan and light on separate switches requires running a 3-wire cable (14/3 or 12/3 NMD90) from a double-gang switch box to the fan/light unit — but in Ontario, this is work that must be done by a licensed electrician with an ESA inspection. While the concept is straightforward, bathroom electrical work involves wet-location safety requirements that make it a professional-only job under the Ontario Electrical Safety Code.

That said, understanding how it works helps you communicate with your electrician, plan your renovation, and make informed decisions about your bathroom's electrical layout.

Why Separate Switches Matter

Having the exhaust fan and light on separate switches is far superior to the single-switch setup found in many older GTA bathrooms. When fan and light are on the same switch, the fan only runs when the light is on — meaning homeowners often turn off both to save energy or avoid fan noise, leaving the bathroom unventilated. In Toronto's humid summers and during long, steamy showers year-round, this leads to persistent moisture buildup, peeling paint, and mould growth — particularly in interior bathrooms without windows, which are common in GTA condos and many Toronto homes.

Separate switches let you run the fan independently, including after you've finished showering and turned off the light. Even better, many GTA homeowners and electricians now opt for a humidity-sensing switch for the fan — a smart switch (such as the Lutron Maestro MS-OPS5MH) that automatically turns the fan on when humidity rises and off when it normalizes. This eliminates the reliance on the homeowner remembering to run the fan.

How the Wiring Works

The basic concept uses a 3-wire cable (which actually contains four conductors: black, red, white, and bare ground) between the switch box and the fan unit. The black wire carries switched power from one switch to the fan motor. The red wire carries switched power from the second switch to the light. The white wire is the shared neutral return, and the bare copper wire is the ground. Both switches share a common hot feed from the circuit breaker, and the fan unit has separate connections for the motor and light.

The switch box needs to be a double-gang box to accommodate two switches side by side. If your existing bathroom has a single-gang box, your electrician will need to enlarge the opening or install a new double-gang box — a straightforward task when walls are open during a renovation but more involved if the walls are already finished.

Circuit Requirements

The Ontario Electrical Safety Code requires that bathroom circuits be properly sized for the load. A bathroom exhaust fan typically draws 0.5–1.5 amps, and bathroom lighting draws 1–3 amps depending on the fixtures. The combined load is well within the capacity of a 15-amp circuit, but your electrician will verify the total circuit load including any other devices on the same circuit.

If your bathroom renovation includes a heated floor system, that requires its own dedicated circuit (typically 15 or 20 amp depending on the mat size) with a GFCI breaker — it cannot share a circuit with the fan or lighting. Similarly, bathroom receptacle outlets in Ontario must be on a dedicated 20-amp circuit separate from the lighting circuit.

The Right Time to Do This

During a bathroom renovation is the perfect time to upgrade from a single-switch fan/light combo to separate switches. When the walls are open for tile work, plumbing, and waterproofing, running the 3-wire cable from the switch location to the fan location is relatively simple and inexpensive — typically $200–$400 in additional electrical labour beyond what you'd pay for a standard fan installation.

If you're not doing a full renovation, an electrician can sometimes fish the cable through existing walls without opening them up, though this depends on the wall construction and accessibility. In GTA homes with finished basements below, accessing the bathroom wiring from below may be feasible.

Fan Sizing While You're At It

Since you're upgrading the switching, it's worth ensuring your fan is properly sized. The Ontario Building Code requires mechanical ventilation in all bathrooms, with a minimum capacity of 50 CFM for a standard bathroom. Size the fan at 1 CFM per square foot of floor area, with a minimum of 50 CFM. For bathrooms with soaker tubs or steam showers, 80–110 CFM is recommended. Quality fans from Panasonic, Broan, or Delta operate at low noise levels (0.5–1.5 sones) and won't discourage daily use.

All bathroom electrical work in Ontario requires an electrical permit and ESA inspection. Your licensed electrician will handle the permit filing and coordinate the inspection during your renovation timeline. Find local bathroom renovation contractors through the Toronto Construction Network to ensure your bathroom electrical work is done safely and to code.