How To Replace Or Install A Bathroom Fan

1. Determine Fan Size and Capacity

Before removing a bathroom exhaust fan, note any markings and measure its exterior profile. These may be useful in determining which type of fan to purchase as a replacement.

Fans come in various sizes and capacities based on the square footage of the room they service. Most lighting shops and home improvement retailers will carry an array of options. If replacing an existing fan, the simplest option is to replace the older fan with one of equal size.

For new installations in rooms with a standard 9-foot ceiling height, simply calculate the square footage of your bathroom to determine the size of the fan you’ll need.

In general, fans sizes can be broken into three categories:

• Small fans can accommodate up to 70 square feet of space, best for smaller bathrooms.
• Medium fans can ventilate between 70 and 100 square feet.
• Large fans are best for applications where more than 100 square feet need ventilation.

2. Remove the Old Exhaust Fan

Turn off the electricity to the room/house at the breaker box. With the fan running, remove/loosen fuses or flip breaker switches until the fan stops. Leaving a note on the electrical panel so no one else turns the power on while you’re doing the replacement is advisable.

Wearing goggles to avoid debris in the eyes, use a screwdriver to remove the grill from the old exhaust fan motor. Use a circuit tester to verify that there is no electricity currently flowing to the exhaust fan.

If a plastic electrical connector or plug is visible, disconnect the fan’s wires—this step may come later after removing the exhaust fan assembly. Use a screwdriver to remove the screws holding the old exhaust fan in place, taking special care to support the fan to ensure it doesn’t fall or break free from the remaining screws.

Once able to lower the exhaust fan assembly, you should have access to any ducting attachments or other wiring harness that may be holding it in place. Set the old exhaust fan assembly aside.

3. Remove Old Exhaust Fan Housing

Unless you’re replacing your old fan with a replica or upgraded model that uses the same housing and bracketry, removing the old exhaust fan housing using a screwdriver will likely be required. Remove any hardware holding the old housing in place, as well as the housing itself.

4. Trace and Cut for Any Hole-Size Adjustments

Hold the new exhaust fan assembly over the hole left by the old fan and trace around its perimeter to establish the size and shape of the hole you’ll need to cut in the ceiling drywall.

Using an oscillating saw and proper protective equipment for your eyes and hands, cut along the traced line to create an opening the appropriate size for your new exhaust fan. It’s incredibly important to ensure you will not hit plumbing or electrical lines on the other side of the drywall.

If installing the exhaust fan system for the first time, you may also need to cut away material through the attic or crawl space above the bathroom in which you’re working, making cuts to accommodate the fan motor assembly and ducting directly above the ceiling hole in the bathroom. Use your oscillating saw, a utility knife, and mask/respirator, gloves and goggles for this part, as you’ll be working in a dusty space likely filled with fiberglass insulation.

5. Install New Fan Housing

Place your new exhaust fan housing over and inside of the newly cut hole and verify that all lengths and angles of the hole appear correct. If so, proceed with the installation of the housing according to the manufacturer’s installation instructions. Any screws used to secure the housing will need their holes pre-drilled using the housing brackets as a template for the holes.

After pre-drilling and properly installing the new fan housing, check to ensure all housing pieces are secure and capable of bearing weight.

If this is your first time installing the exhaust fan system, mounting to a joist and potentially some blocking between joists will be needed to help support the weight of the fan and ducting. Do not rely on sheetrock alone to support the weight of any object not designed for such a configuration.

6. Install New Exhaust Fan Motor

Lift the fan motor assembly into place and secure it to the housing brackets using the manufacturer-supplied hardware.

7. Connect Wires for New Exhaust Fan

If the exhaust fan is equipped with a plastic electrical connector or plug, connect it to the corresponding electrical connection point. If the exhaust fan does not have a plastic electrical connector or plug, or if it does not fit the pre-existing wiring, you’ll need to splice the wires together. For this step, turning the power off is not optional.

Begin by clamping the electrical cable to the exhaust fan housing with 6 to 8 inches of wire extending into the box. Next, strip approximately one half inch of insulation from the end of each wire and, using twist-on electrical connectors, connect the wires (white to white; red or black to black).

Connect the bare copper wire with a ground screw to the plate at the electrical splice box. Be sure to staple the cable to a joist or vertical framing member within 12 inches of the cable clamp.

If you lack confidence in general wiring principles or any part of this step seems like a foreign language, contact a licensed electrician for this portion of the job. Regardless, to be above-board and up to code, all electrical work should be reviewed by a local building department’s electrical inspector.

8. Check ducting to ensure fitment

For simple installations and replacements, no modifications should be necessary to existing ducting. However, if ducting is damaged or incorrectly connected to the new exhaust fan, now is the time to remedy those issues.

Likewise, if this is the first time an exhaust fan system is being installed, a path for ducting to the exterior of the house will need to be determined and cleared. Attach an aluminum elbow to the fan’s exhaust port, and then run as direct a route as possible to the exterior vent, using as few turns as possible. Any vents should be properly sealed and shrouded at the building’s exterior.

9. Seal gaps, replace insulation, restore appearance

Using flexible caulk, seal the area around the fan assembly to ensure no air gaps at the ventilation point and to minimize the sound and deteriorating effects of vibration when the fan is running.

In the attic or crawl space, replace any displaced insulation and cover the new exhaust fan’s housing.

In the bathroom itself, restore power and test the fan. If the fan is loud, disconnect power and ensure the fan is seated flat and that all mounting is securely fastened—most vibrational noise is caused by a poor fastening or seating of the fan assembly. If the fan runs quietly, you’re ready to complete the job.

Install the mounting springs and the new fan’s decorative cover or grill. Use your putty knife to patch any marks made in the course of installing the replacement fan and touch up with matching paint.