How to Install a Bathroom Vent

In just three hours, you can replace your noisy fan with a quiet, high-capacity unit that will keep your bathroom fresh and healthful.

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A vent fan works hard to remove moisture, odor, and mold spores. But eventually, it wears out. The signs? Your mirror is foggy, mold creeps into your shower stall, or the fan roars like a coffee grinder. New fans are quieter and more effective than ever—and they are relatively easy to install. Our how-to instructions make it easy to replace your old vent and get your bathroom up and running again. 

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Before You Begin: How to Buy a Fan

When choosing a fan, make sure it meets the cubic feet per minute (cfm) capacity for your bathroom. To find your bath's cfm, measure the floor area and multiply by 1.1 for an 8-foot ceiling, 1.25 for a 9-foot ceiling, or 1.5 for a cathedral ceiling. For example, an 8×10-foot bath with an 8-foot ceiling needs a fan rated for 88 cfm or more (80×1.1=88).

Also consider the sone number, a measurement of sound volume. The lower the sone level, the quieter your fan will be. For reference, a refrigerator produces about one sone, while ambient office noise is about three. New fans also tend to be larger than old units, which means you'll have to cut a larger hole for your replacement fan. You might also need to add an adapter to make the transition from the 4-inch vent pipe outlet of the new unit to the 3-inch pipe from your old fan.

Bonus: Expert Advice on Bathroom Exhaust Fans

What You Need

  • Safety glasses
  • Work gloves
  • Circuit tester
  • Screwdriver
  • Drywall saw
  • Pry bar
  • Strain relief connectors
  • Wire stripper
  • New fan unit
  • Wire nuts
  • Electrical tape
  • Duct tape
  • Vent pipe adapter
  • 1-inch general purpose screws
  • Drill/driver and bits
  • Fan grille

Step 1: Prep the Space

Before you start, prep by clearing out the bathroom and laying a drop cloth. Gather all of your materials in your workspace. Then set up a stepladder or stool so you can easily reach the fan.

Step 2: Turn Off Power

Switch off the circuit breaker serving the vent fan. Flip the wall switch to On to confirm that the power is off. Remove the grille and pull out the plug that supplies power for the motor. Insert a circuit tester into the plug receptacle to reconfirm that the power is off.

Step 3: Remove Old Fan or Light

Loosen the fasteners that hold the fan/light unit to the housing. Some prying with a screwdriver or hammer might be necessary to remove the unit.

Step 4: Enlarge Opening

If you need to enlarge the opening, hold the housing of the new unit on the ceiling to mark cut lines. Trace around the housing with a pencil. 

Step 5: Cut Around Housing

Use a drywall saw to cut the opening, being careful not to damage any hidden wires or pipes.

Step 6: Detach the Housing and Add Strain Relief

Unfasten the screws holding the housing to the ceiling joists or, if held by nails, use a pry bar to release it. Attach a strain relief connector (it might not come with the fan) to the cap of the housing junction box. Fish the wires through the connector and tighten screws.

Step 7: Connect the Wires

Connect the wires to the new fan unit, beginning with the ground (a green-insulated or copper wire). Join white to white and black to black. Hold the wires side by side and twist on a wire nut. Wrap the wire nut with electrical tape, overlapping the bottom of the nut and the wires. Push the wires into the junction box and attach the cover.

Step 8: Install the Fan

Slide the unit into the ceiling cavity. Snap on the vent pipe adapter. Attach the housing and fasten it to a joist using 1-inch general purpose screws. You might need to drill holes in the housing for the screws. Close and fasten the cover of the wiring junction box. Insert the fan/motor into the housing and tighten the fasteners. Plug unit into receptacle on the housing junction box. Switch on the power at the breaker box and test the fan. Attach the new fan grille.

Bonus: Tips for Replacing a Vent Fan

  • Work from an attic if you can. Lay a piece of plywood across the joists as a work platform.
  • Make an S-shape hook from a wire coat hanger to hold the fan housing as you work.
  • For safety's sake, wear protective goggles to defend your eyes from dust and debris, and gloves to avoid the sharp metal parts of a fan unit.
  • Most old fans have a 3-inch vent pipe, and new fans have a 4-inch vent pipe. Using duct tape on both ends, attach the vent pipe adapter to the new vent pipe of the fan.
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