Foggy bathroom mirrors are not just annoying. The moisture steamy showers and warm baths release into the air can cause serious problems if allowed to build up in the home. Installing a bathroom exhaust fan will whisk away moisture, reduce the growth of mold and mildew, and keep the air circulating for a fresher and more pleasant bathroom. This helpful guide will cover how to properly install a bathroom exhaust fan, including all of the things you need to before you get started, including:

  • The tools and materials you’ll need
  • How to install (or replace) a bathroom exhaust fan
  • Common bathroom fan installation mistakes
  • How to tell when it is time to replace a bathroom exhaust fan
  • Additional answers to common questions on bathroom exhaust fans

Things to know before getting started

If your home does not have a fan, or if the existing fan is old and running poorly, you may be thinking about installing a new one. Whether or not you should do it yourself depends on a few things, such as your own experience and the scope of the work needed for the project.

Installing a bathroom exhaust fan is complex and requires a variety of skills, including carpentry and electrical work. The team at This Old House rates this as a moderate to challenging project that will take between 6 and 8 hours to complete.

In addition to your own experience and comfort level with the work involved in installing a bathroom fan, it is also wise to carefully evaluate your home’s structural layout, especially if there is no existing fan. Planning where the fan will be located in the bathroom to the placement of the exterior vents is a crucial step to take before getting started.

How to install a bathroom exhaust fan

Before deciding whether to hire a professional or do the work yourself, it is useful to review the entire process of installing a bathroom exhaust fan and other important considerations.

Understanding the various tasks required is the starting point. Depending on the age and construction of the house, tasks may include carpentry, plastering and/or drywall repair, and electrical work. Here is an overview of the tools, materials and tasks needed to install a bathroom exhaust fan.

Tools you will need to install a bathroom exhaust fan:

  • Safety glasses and gloves
  • Drill with a hole saw attachment
  • Screwdrivers
  • Wire strippers
  • Non-contact voltage tester
  • Caulking gun and caulk
  • Stud finder
  • Jigsaw or drywall saw
  • Ladder


  • Bathroom exhaust fan
  • Ductwork and an exterior vent with a cover
  • Flexible insulated duct
  • Duct tape

Broan-NuTone & Panasonic are the top bathroom exhaust fan suppliers.

Here’s a comparison of product specs:


Noise LevelGenerally slightly louder, although higher-end models offer quiet operation.Known for quiet operation, with many models boasting low sone ratings.
CFM RatingWide range of CFM ratings to suit different bathroom sizes and ventilation needs.Wide range of CFM ratings, but focus on higher CFM models for better ventilation.
Energy EfficiencyOffers Energy Star certified models, but efficiency varies across models.Strong focus on energy efficiency, with many models exceeding Energy Star standards.
FeaturesBasic models focus on ventilation, while higher-end models offer features like lights, humidity sensors, and timers.Offers a wider range of features across all price points, including motion sensors, nightlights, and built-in Bluetooth speakers.
Price PointWider range of price points, with budget-friendly and premium options available.Generally slightly more expensive than Broan-NuTone, but premium features contribute to the cost.
DurabilityReliable and long-lasting, with solid build quality.Known for durable construction and high-quality components.
WarrantyVaries depending on model, typically ranging from 3 to 5 years.Generally longer warranties compared to Broan-NuTone, some models offering up to 7 years.
InstallationRelatively straightforward installation process.Installation may be slightly more complex for models with advanced features.
Customer ServiceGood customer service reputation, but some user reports of difficulty reaching support.Excellent customer service reputation, known for prompt and helpful support.

How to replace a bathroom exhaust fan (or install a new one) step by step

The installation of a bathroom fan, whether you’re replacing an old fan or starting totally from scratch, can be broken down into four key steps:

  • Selecting the location for the fan and placing it, which involves choosing the best location in the bathroom for the fan (or fans) as well as the first step of installation. (See Steps 1-4)
  • How to vent a bathroom exhaust fan, including ensuring the ventilation terminates outside. (See Steps 5 & 6)
  • Connecting the fan to electrical power (Steps 7 & 8)
  • Sealing and insulating the fan (Steps 9 & 10.)

How to place the bathroom fan:

  1. Start by selecting the location for the fan. The fan should be placed between the shower and toilet to ensure efficient circulation of air and ventilation of moisture. Ideally, the fan should not be directly over an air register or window, as you want the fan to pull air through the room when it is running.
  2. Mark where you will cut the ceiling. Marking the ceiling to create a guide for yourself will help ensure accurate cutting. Use the fan housing as a template. Before you start cutting, double-check the attic on the other side for joists, cables or wires that may be in the path of the saw.
  3. Cut the opening. Put on your safety glasses to protect your eyes from any falling debris and, using either a jigsaw or a drywall saw, cut out your marked area.
  4. Place the fan. The next step is to secure the fan to the ceiling joists or framing, using screws to hold the fan in place. In the event the location you chose does not align with the closest joists, additional framing may be needed.

How to vent a bathroom exhaust fan:

  1. Connect the fan to the duct. Attach a duct to the fan’s outlet, using duct tape or clamps to secure it. The duct should vent outside, not into an attic or other space within the home. Some of the earliest exhaust fans were originally vented into attics, however, today’s building codes require external venting. If you are replacing an older fan, evaluating the venting to ensure the fan exhaust is venting outside is important.

Note: Make sure the venting duct is as short and straight as possible to maximize efficiency.

  1. Install the external vent. If the home does not already have one, you will need to install a vent on the exterior wall or roof at the end of the duct line. Use caulking to thoroughly seal around the exterior vent. At this point, it is also wise to install a cover on the external vent to prevent birds and other small animals from entering and nesting within the vent pipe.

How to connect a bathroom ventilation fan:

  1. Wire the electrical connections. The next step is connecting the fan to the switch. Double-check that the power is off during this step. Important: if you do not have electrical experience, it is wise to hire an electrician for this work. Connect the fan’s wires to the house wiring. Usually, the colors of the wires are your guides, e.g. connect black to black, white to white, and ground to ground. Secure the connections using wire nuts, then insulate them with electrical tape. Place the wires inside the fan housing and cover with the fan grill.

Note: If the fan has a light, heater or other features, additional wiring may be required.

Bonus Tips:

  • Look for bathroom exhaust fan models with dimmable lights to offer greater control over bathroom ambiance
  • Choose a heater wattage appropriate for your bathroom’s square footage
  1. Testing. Turn the power back on and test the fan for proper operation.

How to seal and insulate a bathroom fan:

  1. Sealing. Use caulk to seal the fan housing’s edges to prevent moisture from entering the attic.
  2. Insulation (optional.) Insulate the area around the fan housing in the attic to prevent condensation and energy loss.

Remember, this is a general guide. Specific bathroom exhaust fan models and bathroom configurations, as well as the age and construction of the home, might require different steps or other precautions. If at any point you feel unsure about the process, it is best to consult with a bathroom remodeling professional. Mistakes are common, and they can be costly to fix.

Common bathroom fan installation mistakes

Homeowners often make several common mistakes when installing bathroom exhaust fans themselves, and these can reduce the fan’s efficiency and the overall health of the home. Here are some of the key mistakes to avoid:

  • Poor venting: One of the most common mistakes is not venting the exhaust fan to the outside. Venting into an attic, soffit, wall, or crawl space can lead to moisture problems, mold growth, as well as damage to the roof and other parts of the structure.
  • Wrong fan size: Choosing a fan that is too small for the size of the bathroom can lead to inadequate moisture removal. It is important to select a fan based on the room’s square footage and the fan’s CFM (Cubic Feet per Minute) rating. (More on this below.)
  • Incorrect location: Installing the fan in the wrong location can reduce its effectiveness. The fan should be placed near the shower or bathtub for maximum moisture extraction.
  • Not thinking about noise: Not considering the fan’s noise level of the fan can result in a disturbingly loud unit. A quieter fan is often more pleasant for regular use. Fan noise levels are measured in sones. According to the Home Ventilating Institute, for quiet ventilation, look for fans rated at 1.0 sones or fewer.
  • Inadequate sealing and insulation: Failing to properly seal and insulate around the fan can lead to air leaks, reducing energy efficiency and potentially allowing moisture to enter the attic or walls.
  • Ignoring electrical safety: Handling electrical connections without proper knowledge or failing to ensure that the circuit can handle the load can be dangerous, and even result in a fire. It is essential to follow electrical codes and, if you are unsure, hire a professional electrician for this work.
  • Not installing a timer or humidity sensor: Timers and humidity sensors are relatively new features, and easy to overlook if it has been years since you looked at new bathroom fans. Fans without timers or humidity-sensing switches depend upon the user to turn them on and off. They may not run long enough to remove all the moisture, or they can run too long, wasting energy.
  • Ignoring local building codes: Not following local building codes and regulations can lead to safety hazards and serious issues when it comes to selling the home.
  • Doing it yourself when you do not have the skills or experience: Installing a bathroom ventilation fan involves cutting into the home’s structure, ventilating the fan to the outside, and considerable electrical work. Attempting to install the fan without adequate DIY skills or knowledge can lead to poor installation, safety hazards, and potential damage–all of which are potentially costly to rectify.

To ensure a proper installation, it is often best to consult with a professional, especially for complex installations in older homes or when dealing with electrical wiring.

How to tell when it is time to replace a bathroom exhaust fan

Bathroom exhaust fans are designed to have long lives of 10 years or more with normal use and minimal maintenance. If your fan is older, or you are unsure of when it was installed, there are a few ways to tell whether it needs to be replaced.

Start by giving the fan a thorough cleaning if you have not done so recently. Cleaning a bathroom fan can help rectify a variety of minor problems, such as noisiness, slow starting and failing to adequately ventilate the room and remove moisture.

Keep an eye on the moisture in the bathroom. Bathroom vent fans are designed to pull moisture out of the bathroom and keep air circulating. If you notice dripping windows, moisture collecting on the walls or excessively foggy mirrors that do not clear quickly, it may be time to replace your fan.

A simple test you can perform is the “toilet paper test.” Tear off two squares of toilet tissue and turn on your fan. Hold the tissue squares up to the fan cover. A fan that is running well will hold the tissues to the cover. If the fan is not able to hold the paper up, it is not running efficiently.

How many CFM are needed for a bathroom exhaust fan?

Fans are measured by their capacity to move air, which is measured in Cubic Feet per Minute or “CFM.”  Determining the correct size fan for a bathroom depends upon the size and layout of the bathroom and the fixtures within it.

The Home Ventilating Institute recommends that bathroom exhaust fans should be rated at 1 CFM per square foot of bathroom area as a basic rule. Square footage is easy to calculate–simply multiply the room length by its width. A powder room that is 8 feet long and 5 feet wide, for example, would measure 40 square feet, and need a fan rated at least 40 CFM.

However, for larger bathrooms, the HVI recommends selecting a fan based on the number and type of fixtures using the following guidelines found on their website:

Bath FixtureRecommended CFM
Jetted tub100


Here is an example of how to calculate CFM needed for a larger bathroom with multiple fixtures:

The bathroom is 20’x12′. There is a tub (without jets), a shower enclosure and an enclosed toilet. Note: enclosed toilet rooms or water closets must have either an operable window or a fan for ventilation.

In this example, each bath fixture requires 50 CFM, for a total of 150 CFM. There are two options for properly venting this bathroom:

  1. Install three 50 CFM fans– one over the tub, one in the shower, and one in the water closet. This method is very effective and will provide ventilation where and when it is needed.
  2. Install one 150 CFM fan. The air will then be pulled through the entire room and exhausted at a central location. This assumes the enclosed toilet has a window.

The guidelines from the HVI are a general rule of thumb, and there are several additional factors to consider when calculating the CFM rating your bathroom project requires, such as:

  • Ceiling height: Rooms with very high or vaulted ceilings and require even more powerful fans for proper ventilation
  • Length of the ductwork: Long duct runs, or ducts with numerous bends and elbows, which reduce the efficiency of the fan. This is why evaluating the layout of the home is critical before selecting a fan–if the bathroom has a long duct, a fan with a higher CFM rating will be needed
  • High moisture output bath fixtures: Steam showers or large showers with multiple heads produce more moisture than ordinary bath fixtures and may require fans with a higher CFM rating
  • Layout constraints: Sometimes the bathroom layout or design might prevent a single fan from being effective. For instance, if there are partitions or distinct areas that are not easily reached by the airflow from one fan, additional fans might be preferable.
  • Performance and noise: In the example above, a single large fan is one of the options. However, using multiple fans with lower CFM ratings can sometimes be more efficient and quieter than using a single, larger fan, and provides the flexibility of using the added ventilation only when needed.
  • Spot ventilation: In some designs, it is beneficial to have spot or localized ventilation by placing a fan directly above a bath fixture. For example, a fan directly above a shower or tub can effectively remove moisture right at the source, while another fan can handle the rest of the bathroom.
  • Local building codes: Depending upon where you live, local building codes can have specific requirements based on bathroom size or other factors.

When deciding whether to use multiple fans, remember that each will need to be properly vented to the outside to prevent moisture issues in other parts of the building. Additionally, the total CFM of all fans should meet the ventilation requirements for the size and use of the bathroom. Always consult with a professional or refer to local building codes to ensure that your plan–including the ductwork, exterior vents and wiring–is adequate for the room and fully compliant.

Remember that it is often better to err on the side of a slightly higher CFM rating than to have inadequate ventilation.

Should I install a bathroom exhaust fan in an older home?

Homes built in the 1950’s and earlier generally did not have bathroom exhaust fans included in their original design and construction. Natural ventilation through windows and roof vents was more commonly relied upon, and the construction methods and materials used in older homes often allowed for more natural air exchange. As building codes and practices evolved, along with understanding of the role ventilation plays in moisture and mold control, bathroom exhaust fans became more popular. Today, some form of bathroom ventilation is now required by most local authorities for new construction.

Retrofitting an older home with an exhaust fan can be challenging. Installing ductwork, vents, and electrical connections in an existing structure, especially one not originally designed for such features, can be difficult and costly. However, for owners of older properties, installing a bathroom exhaust fan can be a valuable upgrade, especially as part of a comprehensive bathroom remodel. However, it is important to assess the structural and electrical implications of such an installation, and in many cases, consulting with a professional is advisable.

Does installing a bathroom fan require a building permit?

Do not forget to check and see if your local government requires a building permit. If the installation involves significant electrical work, structural changes, or modifications to your home’s exterior, a permit is more likely to be required. Simple replacements or minor installations might not need a permit. Additionally, if your home is a historical building, or you live in a regulated community such as a condominium or homeowners association, there may be additional requirements or restrictions.

Unpermitted work can cause problems down the road. In some cases, if you are found to have done work without a required permit, you may be fined or required to remove and re-do the installation. You can also unwittingly create an insurance liability for yourself, as work done without a permit may not be covered by home insurance in the event of related damage. Finally, unpermitted work can cause headaches years later when the house is sold.

Even if a permit is not needed, an inspection of the work might be a good idea for safety reasons, especially for electrical connections.

A big job that is worth the effort

Installing a new bathroom exhaust fan is a big task, but so is the payoff. Keeping the air circulating and moisture in check makes the bathroom feel fresher and cleaner, keeps mold and mildew at bay, limits damage caused by dampness and creates an environment all will enjoy.

With professional guidance and expertise, your bathroom remodeling journey can be a breeze. At Re-Bath, we fully comprehend the intricacies of bathroom renovations and provide tailored solutions that mirror your lifestyle and preferences. Our trusted team of experts ensure that your bathroom makeover is effortless and swift.

Ready for a change? Get in touch with Re-Bath today and make your dream bathroom a reality sooner than you ever imagined.