How to Install a Bathroom Exhaust Fan

bathroom exhaust vent fan
Wil C. Fry / Flickr / CC BY-NC-ND 2.0

Installing a bathroom fan is just the remedy you need for rooms that never seem to get dry.

While bathroom exhaust fan installation is not the easiest home improvement project, you may be surprised to learn that it is a bit easier than expected and can be accomplished entirely by DIY.

Moisture-laden air is the enemy of bathroom paint, fabrics such as towels and curtains, windows and doors. Expelling moisture–not to mention odors–makes for a far more pleasant bathroom experience for all.  

Before You Begin

Two issues often concern homeowners taking on this project: power and venting to the outside. Most residential bathroom fans use AC 120V electrical lines. The instructions below offer tips for finding live electrical cables and running them to the correct location.  

Venting means that after air from the bathroom is drawn into the exhaust fan; it is blown through a connected flexible duct and out of the house through a hole in the side of the house or roof. Since this is a new installation (not a replacement), your bathroom will not have ducting. However, as long as you can access the area above the bathroom ceiling, you will be able to route the venting outside.

Tools and Materials

  • Bathroom exhaust fan
  • 6 foot ladder to access attic
  • Safety glasses
  • Reciprocating saw
  • Exhaust vent
  • Flexible ducting
  • Cordless drill
  • 1/2 inch drill bit
  • Pencil
  • Drywall jab saw
  • Screws
  • Stud finder
  • Round wall vent or roof vent cap, depending on whether you are exhausting to the side wall or roof.
  • Exterior grade silicone caulk

Instructions for Installation

To begin, you will need a 6 foot ladder, a light and filter mask. Turn off electricity to the existing ceiling light by flipping off the breaker at the service panel. Locate your attic access door and enter it with the ladder.

Find the Power

The vent fan will be installed in the ceiling. You may already have power running to the exact point where you intend to install the bathroom vent fan. Depending on your local electrical code, you may be able to share your bathroom lighting circuit with the fan. The bathroom lighting circuit usually supplies power to your bathroom's ceiling light. Alternatively, you can substitute the light for a fan/light combination.

If your code requires you to run a dedicated circuit for the fan, you can run a new cable from the service panel to the bathroom ceiling area. If you don't feel comfortable setting up new circuits and working with the service panel–a dangerous area–this would be time to contact an electrician to complete this task.

Locate the Vent Point

Air exhausted by the fan must exit outdoors. So you will need to run a duct from the fan to either the roof or a side wall. If possible, run the duct to a side wall, as this helps you avoid shingle work and the possibility of roof leaks.  

Ideally, the rule of thumb for vent location is to choose a spot that:

  • Affords a direct route from the fan to the outside.
  • Is 6 feet long or less distance from fan to exit point.
  • In the bathroom interior, is located close (but not in) the shower, tub or shower/tub combination, as this is the area that produces the most moisture.
  • Avoids sharp elbow bends in the ducting.

Drill a locator hole at the center of the intended location.

Cut Exterior Vent Location

Depending on where you intend to exhaust to the exterior, access either the side wall or roof of the house.

Bring your round vent (for walls) or vent cap (for roofs). Also bring your reciprocating saw, cordless drill, pencil and silicone caulk. Situate the round vent or vent cap across the locator hole. With the pencil, scribe a circle where the vent or cap will fit.  

Use the reciprocating saw to cut the circle. Use the locator hole as a start point for the saw blade. Attach the round vent or roof cap with screws, first applying silicone caulk to ensure a watertight fit.

Cut Interior Opening for Fan

Use the stud finder to locate the joists in the bathroom ceiling and lightly mark with a pencil.

If the fan comes with a paper template, use this to mark the intended location of the fan in the ceiling. If there is no template, use the metal fan housing itself (leave the fan assembly out for now). Many bathroom fans screw directly to the side of the joist. If so, place the template or housing parallel to a joist when making the cut lines.

Cut out drywall carefully with the jab saw.

Attach Fan to Joist

Access the attic and bring your light, cordless drill, screws and bathroom fan housing (the metal box that holds the fan).  

Place the fan in the cut-out hole so that the bottom edge of the fan is flush with the bottom of the ceiling drywall. You will need a partner for this step, as you cannot see the ceiling from this position.

Screw the fan into the side of the joists with the cordless drill.

If you cannot use the side of a joist for attachment, your fan may come with suspension brackets. If not, you can purchase these separately. They will allow the fan to be suspended in a position that is not adjacent to a joist.

While you are still in the attic, fit the electrical wire through the side of the housing so that roughly 7 in. of wire extends into the housing.

Route Fan to Outside

Go back down to the bathroom and verify vertical placement of the fan. Gather your flexible ducting and take it back into the attic.

Attach flexible tubing to the fan and the vent. Ensure that the tubing runs as smoothly and directly as possible.

Attach Fan to Housing

In the bathroom, insert the fan unit into the housing per the manufacturer's instructions. At this point, you will hard-wire the electrical wire to the unit.

Attach the fan grille to the face of the housing. Turn circuit breaker back on. Return to the bathroom and test the fan by turning on the switch.