How to Install an Auto-Sensing Bathroom Vent Fan

Today’s new vent fans include a sensor so that when someone enters the room, it turns on the light and monitors the humidity. It automatically turns on the vent fan if the humidity level rises and turns it off when the air returns to normal. Assuming that no new electrical line is needed and the ductwork is already in place, you can do this job yourself. Because you'll be working in the bathroom and the attic, however, having someone to help you is more convenient.

Before you get started, carefully read the instructions that come with the unit and identify the parts and hardware. If the unit is located in a bathtub or shower enclosure or within 5 feet of a shower head, the circuit must be GFCI-protected.

Before you begin, shut off the power to the bathroom at the circuit breaker or fuse panel.

After you remove the old unit, use these directions to install the new unit:

  1. Position the unit so that its longer dimension is parallel with the joists, or the unit may not fit between the ceiling framing.

    Disassemble the motor from the fan housing, which lightens the weight you have to hold over your head while you work.

  2. Fasten the fan housing in the opening and connect the wires to both the fan/light and switch.

    Connect the wires according to the manufacturer's instructions for like-colored wires: black to black, white to white, and green or bare wire to the ground wire.

    The unit is likely to be installed in a switch loop. If that’s the case, the white wire running between the switch and the unit is hot and should be marked at each end with black tape or marker to indicate that it’s hot. Fan/light leads are likely to be colors like red or yellow — anything other than black and white.

  3. Use the extendable mounting brackets (if provided) and attach them to the joists from the attic. Then crimp the guides that hold them to the housing.

    If the fan is aligned next to a ceiling joist, some units can be fastened directly to the ceiling joists through the holes or slots in the housing. In this case, remove the brackets so they won't rattle when the unit operates. Double-check that the height is such that the edge of the housing is flush with the finished ceiling.

  4. With the housing securely in place, reinstall the fan motor and tighten all connections.

    The unit has separate plugs on the housing for the fan and light (they're usually color-coded for easy identification) to connect them.

  5. Reconnect the ducting.

    Ensure that the unit's damper moves freely and opens fully after you make the connection.

  6. Wrap the joint with duct tape, install the grille, and insert the bulbs and the light's diffuser.

    The duct tape ensures an airtight seal.

Restore the power at the circuit panel and test all functions. The unit's sensors are preset for sensitivity and timer duration at the factory, but you can readjust them to suit your lifestyle.

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