Build.com For Pros: How to Install a Bathroom Exhaust Fan

Excess moisture and humidity can fog up mirrors and make bathrooms uncomfortable spaces. Odors linger in bathrooms, and even worse, enter adjacent bedrooms or shared rooms. Installing a bathroom exhaust fan can help alleviate these issues. 

With a variety of bath fans and bath fan kits on the market today, putting one in place doesn't have to be overly complex if you're an experienced builder or contractor.

Preparing to Install a New Exhaust Fan

Before you bring in the new exhaust fan, it’s important to make sure the bathroom is equipped to handle the appliance. Some specific preparations ahead of the install can help ensure the safe, daily operation of the exhaust fan.

Locate Your Exhaust Route

An exhaust fan installed in a bathroom must vent air outside. In many cases, a fan is vented outside through the roof via the attic. Allowing your fan to vent into a closed attic will result in problematic moisture buildup.

However, there are other bathroom exhaust fan venting options available. If venting through the attic is not possible on your project, you'll need to vent through another sidewall. These secondary locations are typically installed when a home is built and fairly easy to locate.

In older home renovations, further changes may need to be made for proper ventilation.

Evaluate Your Electrical

Most bathroom exhaust fans are wired to an existing switch in the bathroom. Combining the function of a particular switch, like a shower light and exhaust fan, is quite common. 

If you're replacing an old fan without a light with a model that does, consider installing a double switch. This will provide the end user with separate controls for the overhead light and fan

Installing a New Fan With No Existing Fan

Many modern bathrooms have exhaust fans that may simply need updated with current models. If you're working in a bathroom that doesn't have an existing exhaust fan, you'll need to do a few things before you can use the installation procedures outlined here.

1. Locate your power source. In most bathrooms, a fan can be wired to an existing light switch. For more independent control, consider re-wiring a single switch to a double switch that can control both your light and fan.

2. Locate your vent point. All air removed via your exhaust fan must be vented outside. This is done through the attic and roof or a sidewall duct. When choosing your vent point, your goal should be the shortest path, ideally no more than four to six feet from the exhaust fan to outside.

3. Create an exterior vent location. Choose your exterior exhaust point and cut an exterior vent. Typically, round vents are used for walls and vent caps are used for roofs. A reciprocating saw is the most common tool for cutting an exterior vent, but this can vary based on the housing material you're working with.

4. Cut the opening for your bathroom fan. Many fans come with templates that can guide you when creating an interior opening for your bathroom exhaust fan. If the fan you're using did not come with a template, you can use the metal fan housing without the heavy assembly as the template.

When working with drywall, use a jab saw to create the vent opening. When finished, use silicone caulk to create a weatherproof seal around the housing edges. Once the area is prepared, you can then move on to the installation.

Removing the Old Exhaust Fan

Learning how to replace a bathroom exhaust fan starts with removing the old one.

Here's a step-by-step guide to remove an exhaust fan that will work for most exhaust fan models:

Step 1:

Turn the breaker off that controls the fan. Use your circuit tester to make sure the power is off to the fan.

Step 2:

Locate the motor in the fan housing and remove it. Use a screwdriver to remove screws holding it in place. Disconnect the motor from any wiring attaching it to the fan housing.

Step 3:

Remove the fan housing from the ceiling by loosening the screws attached to the ceiling joist. If you don't see screws, you may need to remove metal brackets holding the fan in place. These are typically located in the attic. If you don't have access to the attic, you may need to cut the brackets away from a safe ladder position.

Step 4:

Disconnect any wiring in place and move the housing so you can access the duct and electrical connections. Disconnect the exhaust duct and remove the fan. Make sure you keep the house wiring within reach so you're ready for your new fan installation.

How to Install a New Exhaust Fan

When you're installing a bathroom exhaust fan, you'll need to vent through the attic and roof or through a sidewall. The installation process for each method varies. Follow the step by step instructions below depending on the method that you're using for your project.

Venting Through the Attic

Often the best choice, and the most common, is venting your bathroom exhaust fan through the attic. In an upstairs or single-floor space, this method can help keep problematic moisture at bay when the correct fan is used.

To install a bathroom exhaust fan that vents through the attic:

Step 1:

Check that the ceiling hole from the old fan is the correct size for the new fan. If the hole is too small, use a keyhole saw to make the appropriate cuts. If the hole is too big, patch the area with drywall filler. You can circle back and repair patched areas with spackling later.

Step 2:

Secure the duct connector to the exhaust fan housing. In most cases, this will simply slide into place with little effort on your part.

Step 3:

Attach the housing brackets from the ceiling fan supplies to the ceiling joists from the attic. Next, insert the brackets into the correct slots on the housing, using screws or nails to secure the brackets in place. Secure the brackets to the housing if instructed by the manufacturer.

Step 4:

Connect your electrical. This typically requires you to remove the wiring cover on the fan housing and remove a knockout plug with a screwdriver.

Step 5:

Secure the house wires by pushing them through the clamp from the fan kit. Use wire nuts to connect the fan wires to the matching house wires. Typically, white is neutral and black is hot. Green is commonly the ground.

Step 6:

Push the wires up into the housing and secure the wiring cover to the exhaust fan housing using the supplied screws.

Step 7:

Secure your duct to the duct connector using code-approved HVAC tape. Ensure that the duct is venting outside.

Step 8:

Turn the power back on and check that the fan is working properly. Install the grille and touch up the ceiling if needed.

Installing an Exhaust Fan Without Attic Ventilation

Here's a step-by-step guide to install a bathroom exhaust fan for ventilation when you don't have access to the attic:

Step 1:

Check that the current hole for your exhaust fan is the right size. If not, use a keyhole saw to enlarge the hole. Alternately, use drywall and wood pieces to make the hole smaller. You can patch later if needed.

Step 2:

Make sure that the fan can be mounted to a ceiling joist. Ideally, the old fan was already mounted to a joist you can work with. If not, use lumber to build out the joist so you can attach at least one side of the ceiling fan.

Step 3:

Use HVAC tape or a clamp to attach the ceiling fan duct to the duct in the ceiling. This ceiling duct should vent outside. Use a screw to attach the duct connector to the edge of the hole in the ceiling. This will help make sure it lines up with the exhaust on the final fan housing.

Step 4:

Connect your electrical. You'll likely need to remove the wiring cover on the fan housing and remove a knockout plug with a screwdriver.

Step 5:

Secure a cable clamp to the hole on your wiring cover. Now you can secure the house wires by pushing them through the clamp from the fan kit. Use wire nuts to connect the fan wires to the matching house wires. Typically, green is usually the ground, white is neutral, and black is hot. .

Step 6:

Push the wires into the housing and connect the wiring cover to the housing using the supplied screws.

Step 7:

Place the fan into the ceiling hole, being careful to properly line up the exhaust with the duct connectors. Use screws to secure the fan and mounting flange.

Step 8:

Turn the power back on. Once you have checked to make sure the fan is working properly, install the exhaust fan grille. As part of the project cleanup, touch up the ceiling as needed.