A bathroom exhaust fan wired on its own circuit or sharing a circuit with the bathroom light uses 14/2 NM-B cable on a 15-amp single-pole breaker. Most exhaust fans draw only 0.5 to 2 amps at 120 volts, a tiny fraction of what 14 AWG wire on a 15-amp circuit can safely carry. The exception is exhaust fans with a built-in electric heater: any fan with a heating element rated above 1,440 watts requires a dedicated 20-amp circuit with 12/2 NM-B wire because heating elements are a continuous load and must be sized at 125 percent of rated current under NEC 210.19(A)(1).
Standard Exhaust Fan: 14/2 NM-B
A standard bathroom exhaust fan without heating draws 30 to 75 watts (0.25 to 0.6 amps at 120 volts). Wiring this fan requires running 14/2 NM-B from the panel or from a junction box on an existing 15-amp bathroom lighting circuit to the fan location in the ceiling. The black (hot) conductor connects to the fan hot lead, the white (neutral) connects to the fan neutral lead, and the bare copper ground connects to the fan ground terminal or the metal housing. A wall switch in the circuit opens and closes the hot conductor to control the fan independently of the light, or the fan and light can share a single switch.
Fan and Light on Separate Switches
When the bathroom fan and light are controlled by separate switches (a common and preferred configuration for independently timed use), the cable from the switch box to the fan location may need to be 14/3 NM-B rather than 14/2 NM-B. The 14/3 cable provides three insulated conductors: one for the fan switch leg, one for the light switch leg, and the white neutral, plus a bare ground. This allows one cable to serve both the fan and light from a two-switch box without requiring two separate cable runs from the switches to the ceiling.
Combination Fan and Heater Units
Bathroom combination units that include a fan, light, and electric heater in a single ceiling fixture commonly have a heater element rated at 1,000 to 1,500 watts. A 1,000-watt heater draws 8.3 amps at 120 volts continuously, which on a 15-amp circuit leaves only 6.7 amps of remaining capacity. Applying the NEC 125-percent continuous load factor, a 1,000-watt heater requires a minimum 10.4-amp rated conductor, which is safely covered by 14 AWG on a 15-amp circuit. A 1,500-watt heater draws 12.5 amps continuously, and at 125 percent requires 15.6 amps, which exceeds the 15-amp circuit rating and demands a 20-amp circuit with 12/2 NM-B. Always check the heater wattage rating on the combination unit before selecting wire and breaker size.
GFCI Requirement
NEC 210.8(A)(1) requires GFCI protection for all receptacles in bathrooms. While an exhaust fan is hardwired rather than plugged into a receptacle, some jurisdictions interpret GFCI protection as required for all bathroom electrical circuits. Confirm the local code interpretation with your building department. A GFCI breaker at the panel protecting the bathroom circuit is the most comprehensive approach and covers all outlets and hardwired fixtures on that circuit.
IB Lighting carries 14/2 and 14/3 NM-B Romex from Southwire and Cerrowire in 50-foot, 250-foot, and 1,000-foot spools. Browse our wire and cable selection or call (800) 674-9019 for contractor pricing. Free Freight Insurance Included on every order.