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:

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• 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

Materials:

• 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:

 

Broan-NuTonePanasonicNoise 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.

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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:

5. 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.

6. 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:

7. 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

8. Testing. Turn the power back on and test the fan for proper operation.

How to seal and insulate a bathroom fan:

9. Sealing. Use caulk to seal the fan housing&#;s edges to prevent moisture from entering the attic.
10. 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 CFMToilet50Shower50Bathtub50Jetted 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 &#;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.

Find Your Local Re&#;Bath

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Connect with your nearest Re&#;Bath to start your bathroom remodel. Schedule a free, in-home design consultation today.

Guide to Bathroom Exhaust Fan Venting Options

By Amanda Lutz

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Bathroom exhaust fans remove excess moisture from your bathroom and push it through the ductwork, away from the building materials that compose your home. A properly installed bathroom exhaust fan also helps reduce the chance of mold and mildew growth and prevents structural damage to building materials vulnerable to moisture.

A bathroom vent fan can&#;t eliminate moisture from your home without the proper installation and venting. If you don&#;t know how to vent your bathroom exhaust fan or want to ensure adequate ventilation, then keep reading to learn about various bathroom ventilation options and building code requirements.

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Importance of Proper Bathroom Exhaust Fan Venting

A bath exhaust fan pumps large amounts of moisture out of your home, but it won&#;t work well if it&#;s not installed correctly. In fact, you must vent the fan outside your home to eliminate moisture and prevent subsequent damage.

If the air from your exhaust fan flows into your attic or crawl space, moisture will remain in your home. The concentrated flow of moist air simply shifts the potential for mold growth and water damage to a different part of your home. All too often, exhaust fans direct moisture into the attic, potentially damaging ceilings, attic floors, roof framing, and roof sheathing. Improper venting is also the cause of mold growth, structural damage, poor indoor air quality, and a shortened life span for your bath fan&#;s motor.

Bathroom Exhaust Fan Venting Options

The best option for venting your fan depends on your bathroom&#;s location, accessibility to the exterior of your home, and local building codes. Regardless of the route, the exhaust duct should be as short and straight as possible to promote optimal airflow.

Venting Through an Exterior Wall

If your bathroom offers access to an exterior wall, venting through the wall is often a better option than a horizontal installation. Through-the-wall exhaust fans are available as kits that include an exterior cover and short duct sections. They vent directly outside through the wall and don&#;t have bends that reduce airflow.

Alternatively, you can use a ceiling-to-wall approach with a fan installed in the ceiling and the vent running to an exterior wall. For this option, the vent usually goes straight across the bathroom ceiling and reaches an outer wall.

For fan installation, cut a section of the wall for the fan and a section on the outside for the exhaust. Trace the exterior of the fan and exhaust housing to size the openings correctly. While you shouldn&#;t need bends for this installation type, sloping the duct slightly downward will limit the potential for condensation buildup in the line. Follow the manufacturer&#;s instructions to install your wall vent fan and the required ductwork safely.

Venting a fan through the wall is a good option for a first-floor bathroom with an accessible exterior wall. However, never position the vent into another interior wall or garage, as this makes it difficult for the vent fan to pull fresh air into the bathroom.

Venting Through the Roof

Venting an exhaust fan through the roof is often the most direct, efficient route. You install the roof vent fan in the ceiling with a vent that travels straight through the attic space and out the roof. While this option allows moist air to travel directly upward through the roof, improper installation can cause leaks where the duct exits the roof. Sealing the vent properly can be challenging and often requires professional installation.

Venting through the roof is a good way to promote increased airflow without bends or turns. It&#;s optimal for single-story homes and second-floor bathrooms. Installation will require cutting a section of the ceiling, attaching the fan to ceiling joists, and cutting a small section in the roof for the duct to exit. If you choose to install the fan and ducts yourself, follow the manufacturer&#;s instructions and seal all openings properly to avoid future leaks.

Venting Through the Soffit

Soffit vent installation is a less common option for venting a bathroom exhaust fan. The installation is similar to venting through the roof but directs ducts through the underside of eaves instead of through your roofing.

Since this option requires you to install the vent on the underside of your roofing where soffit venting is already installed, many municipalities don&#;t allow it. However, it&#;s a good alternative if there&#;s limited attic space or a short distance to the soffit. During installation, be sure to install the vent in the ceiling and direct vents across the underside of the roof. To prevent exhaust air from reentering your home, avoid venting in soffit vents and use an exhaust hood where the duct emerges.

How to Vent a Bathroom with No Outside Access

A centrally located first-floor bathroom can be challenging to ventilate. Yet, it&#;s common for bathrooms in apartments and condos to have no exterior wall or roof access. An alternative option may be necessary for these types of bathrooms. While these options aren&#;t as effective as outside venting, they can improve moisture control.

• Ceiling vent: The most efficient way to allow air to escape from the bathroom is through a ceiling vent. For the best results, install a vent where air will flow through the building&#;s HVAC ductwork.
• Dehumidifier: A dehumidifier removes moisture from the air. Installing one close to water sources can lower humidity levels in the bathroom.
• Recirculating exhaust fan with a charcoal filter: Recirculating fans filter the air through a set of charcoal filters before releasing it back into the bathroom. This can reduce humidity levels and enhance air quality. To maintain the fan&#;s effectiveness, replace the filters every three to four months.

Building Code Requirements for Bathroom Exhaust Fan Venting

Follow all required national and local building codes when installing or modifying bathroom venting. In most cases, bathrooms should have exhaust venting fans or windows. Here are a few common building code requirements for bathroom exhaust fans:

• According to section R303.3 of the International Residential Code, a window in a bathroom used in place of an exhaust fan must be at least 3 square feet in area.
• Section M.2 clarifies that vented air needs to flow to the exterior of the home and not to an attic or other interior room.
• Section M.4 mentions that the fan has to be rated for a minimum of 50 cubic feet per minute (CFM).
• Section R303.4 states that, in some cases, an open window isn&#;t a code-approved substitute for an exhaust fan.

While you can reference these codes during installation, the best way to find the most accurate information on code requirements for bathroom exhaust fan venting is to contact your city or county planning and permitting department.

Our Recommendation

Proper bathroom exhaust fan venting rids your bathroom of odors and moisture-laden air; plus, it helps prevent mold growth and moisture damage in your bathroom and other areas of your home. To direct moist air outside instead of into your attic or other interior spaces, you can vent through an exterior wall, the roof, or soffits.

While venting a bathroom exhaust fan can be a do-it-yourself (DIY) home improvement project, consider hiring a contractor if you don&#;t have the proper tools or time to complete the job.

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Bathroom Exhaust Fan Venting Options FAQ

Can a bathroom exhaust fan vent into the attic?

No, you shouldn&#;t vent a bathroom exhaust fan into the attic because the moist air from the fan will remain indoors. This can cause mold and mildew in the attic, potentially resulting in water damage to ceilings, attic floor joists, attic insulation, rafters, and roof sheathing.

Do bathroom exhaust fans have to be vented outside?

Yes, bathroom exhaust fans must be vented outside to prevent moisture buildup in the attic and other areas of the house. You can vent them through an exterior wall, the roof, or the soffits.

How can you vent a bathroom with no outside access?

You can use a recirculating fan with charcoal filters, a dehumidifier, or a ceiling vent to vent a bathroom without outside access. While these options aren&#;t as effective as external venting methods, they can still help control humidity in the space.

What is the best option for a bathroom exhaust fan venting?

The best place for hot, moist air to exit your home is through your roof. This option typically results in the fewest bends and curves to push moist air outside successfully.

What is the code for venting a bathroom fan?

The code for venting a bathroom fan represents a minimum requirement of a fan capacity rated for a minimum of 50 CFM. Other requirements may apply to your local area. Before beginning installation, contact your city or county permitting department to learn about the full regulations for venting a bathroom fan.

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