Sometimes you need to wire a bathroom fan and light on one switch. Code often requires a fan in bathrooms these days, but you may only have one switch. Or maybe you have two switches but just want one switch to run both. Fortunately it’s easy to do. Here’s how.
This kind of arrangement isn’t a bad idea anyway. It’s safe to assume if someone is in the bathroom, the light is on. And running the fan is the best way to keep mold from growing in the bathroom. Condensation from hot water causes mold, but the water won’t condense if the fan pulls the vapor out.
If you already have lights and a fan on two switches, simply label the wires off each switch, remove them from the switches, and remove the light switches. Tie the equivalent wires together with wire nuts while adding a new length of wire long enough to reach the switch you want active. This new wire is called a pigtail. Get a new 20-amp switch. Run the pigtails to the new switch, then remove the old switch for the fan. You might want to put an outlet there in its place.
What if you don’t have a fan in the bathroom yet?
Your light fixture has black and white wires on it. So does your fan. Mount the fan close to the light fixture, then run the black and white wires from the fan over to the electrical box that feeds the light fixture. Shut off the power to the bathroom from the electrical panel. Then remove the wire nut on the bundle of black wires and tie the fan’s black wire into that. Replace the wire nut. Do the same on the white wires.
For safety’s sake, replace the light switch as well. Get a 20-amp switch, which shouldn’t cost much more than $5, instead of the 75-cent 15 amp switch you probably have. You don’t want the light switch to overheat under the load and potentially cause an electrical fire. Using energy-efficient bulbs in the bathroom will also reduce the load on the switch.
In one of the great ironies of landlording, I once had a tenant complain about some water in the basement after a record-setting rain. To my knowledge the basement had never flooded before. She convinced herself the basement would instantly become moldy. Meanwhile, she did have mold in the bathroom because she never ran the fan. She had an irrational fear of mold where there was none, and didn’t recognize mold where she did. Running the fan all the time would have fixed the problem she didn’t recognize, even if she wouldn’t have appreciated it.