Bathroom Exhaust Fan Buying Guide

Last updated May 6,

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Bathroom exhaust fans improve indoor air quality by quickly venting moist air outside. Removing moisture from your bathroom helps prevent mold and mildew growth, among other types of moisture damage. When choosing the best bathroom exhaust fans for your home, know how to identify and select the right size and features.

This guide explains what to look for so you can choose the best exhaust fan for bathrooms in your home.

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Table of Contents

1. How Do Bathroom Exhaust Fans Work?

2. What Size Bathroom Exhaust Fan Do You Need?

3. Things to Consider

4. Special Features

How Do Bathroom Exhaust Fans Work?

Moisture from hot showers, baths and other fixtures can accumulate on your bathroom walls, windows and cabinets. Without proper ventilation, this moisture can lead to mold and mildew growth, peeling paint, damaged wallpaper and warped walls and cabinetry.

An appropriately sized and installed bathroom exhaust fan will remove the moist air and prevent these problems. Plus, bathroom fans can help improve overall air quality and remove odors.

The best bathroom exhaust fans connect to your home’s existing vent ducts and channel the moist air outside. Some types of bathroom fans only vent moist air to the space in between your ceiling joists or into an attic. While easier and quicker to install, these bathroom fans can contribute to moisture damage elsewhere in your home in the long run. If your local building codes require an exhaust fan in bathrooms, then they also likely require that the fan vents air directly outside, rather than into other parts of your home.

We recommend always venting your fans to the outside and never into an attic or crawlspace.

What Size Bathroom Exhaust Fan Do You Need?

The most important part of choosing a bathroom exhaust fan is determining the right size for your bathroom. A fan’s ability to move air is measured in cubic feet per minute (CFM). The bigger the bathroom, the higher the CFM rating you’ll need. A fan should have a CFM rating high enough to replace the air in your bathroom at a rate of eight times per hour.

To figure out the right fan size, first determine the area of your bathroom. Measure the length and width of your bathroom and the height of its ceilings. Then use those measurements in this formula:

• Length x Width x Height = Bathroom Size

Once you have your bathroom’s size, you can convert it to CFM. Use this formula to determine the minimum CFM rating your bathroom fan needs:

• Bathroom Size x 0.13 = Minimum CFM Rating

If you’d prefer to skip the math, or if your bathroom ceilings are too difficult to measure, check the fan’s packaging. The packaging should tell you the maximum square footage the fan can ventilate. If you know your bathroom’s approximate square footage, you can choose a fan based on the maximum square footage the package says it can accommodate.

Here are some bathroom exhaust fan size tips:

• Most fans are rated from 50 to 110 CFM, but some models designed for large master bathrooms, rec rooms and home theaters can be rated even higher.
• Choose a fan that can ventilate at least 1 CFM per square foot of room. So, for an 80 square foot bathroom, select an 80 CFM fan.
• For bathrooms 50 square feet and smaller, it’s recommended you purchase a bath fan designed for small rooms. In other words, choose under 79 CFM bath fans.
• For medium-sized bathrooms, use 80 to 99 CFM bath fans.
• For large bathrooms that are over 100 square feet but under 150 square feet, use over 100 CFM bath fans.
• For extra-large bathrooms, add 50 CFM for every toilet, 50 CFM for every bathtub or shower and 100 CFM for a jetted bathtub.
• If you are buying fans for a large master bathroom, rec room, home theater or other room over 100 square feet, consider installing multiple fans.

Things to Consider

Noise Level:

The industry standard for measuring the amount of noise a fan makes when it’s in use is called sones. Determine how loud a fan will be based on its sone rating. The lower the sone rating, the quieter the fan will be. One sone is equivalent to the sound of a quiet refrigerator, so a quiet bathroom exhaust fan will be rated at about 1 1/2 sones or less.

Energy Efficiency:

Energy efficient fans will have earned an ENERGY STAR label. Many energy efficient fans will also have low sone ratings, so you can expect them to be quiet. An ENERGY STAR certified fan will use about 60 percent less energy than standard bathroom fans.

Mounting Options:

Bathroom fans are available in three models: those that offer ceiling mounts, wall mounts or both. While the ceiling installation style is the most common, choose the mount type that works best with your bathroom’s layout and your home’s ducts. Typically, top-floor bathrooms and single-story homes use ceiling bath fans, while bathrooms on mid-levels may have to use wall bath fans that vent out the side of the home.

Installation:

Keep these installation considerations in mind when buying a bathroom exhaust fan:

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• Consider replacing a light fixture with a bath fan model that features a light. This will allow you to use the existing wiring and switch.
• If your bathroom fan and bathroom light are installed separately, you will need a combination switch that has two or three controls.
• When installing, remember that fans in top story bathrooms will be ducted through the attic to the outside through the roof or wall. Fans in bathrooms in the first story of a multi-story home are vented through the side of the house.
• If you are replacing or upgrading a fan, the diameter of the duct connector on the new housing may be larger than the size of your existing duct. To maximize performance, try to match your new fan to the duct diameter.
• No cut installation bath fans allow you to easily replace an old fan without making any new cuts in the ceiling or wall.

Special Features

Once you know the size, noise level and mounting type that you want, you can start exploring special features for bathroom fans.

• Bath fans with lights: Replace an existing light or add more lighting to your bathroom with a bathroom fan that includes a built-in light. Some fans come equipped with a night light, so you can use the bathroom at night without disturbing your family.
• Bath fans with heaters: Built-in heaters improve warm air circulation and keep you comfortable even after you step out of the shower or bath.
• Humidity-sensing bath fans: Fans with humidity sensors detect the moisture levels in the air and turn on and off automatically in response.
• Motion-sensing bath fans: Often paired with humidity sensors, a motion sensor will detect movement in the bathroom, turning the fan on as a person enters the room and turning it off after detecting no movement for a set amount of time.
• Bath fans with adjustable fan speeds: Ensure optimal CFM by setting your desired fan speed. If you find the lowest CFM option isn’t venting your bathroom efficiently, change the setting on your fan to a higher CFM.
• Bluetooth-enabled bath fans: Some fans are equipped with Bluetooth speakers that can connect to your smart devices, so you can play music while you enjoy a shower or bath.
• Most bath fans have a damper that reduces backdraft of cold air from outdoors, preventing you from losing heat through your fan.
• Decorative bath fans are designed to blend in with your existing bathroom fixtures. Bath fans with lights can include glass globes that make them look like an ordinary light fixture.

To find the best bathroom exhaust fans for your home, first make sure you know what size you need for your bathroom space. Then you can decide the noise level, installation type and special features that best suit your needs. If you need help identifying a type of bathroom fan or bathroom fan parts, find products fast with image search in The Home Depot Mobile App. Snap a picture of an item you like, and we'll show you similar products.

If you’d rather let a professional select and install a bathroom fan for you, consider our bathroom installation services.

Scope Scope Images Scope

Install an exhaust fan in the kitchen to exhaust steam and cooking odors to the outdoors.

• Install the fan to vent outdoors, not into an attic, crawlspace, or space between floors.
• Choose a smooth metal duct with the diameter specified by the fan manufacturer.
• Install the duct with the most direct route to the outside with as few bends as possible.
• Seal all seams and around ceiling and wall or roof penetrations with mastic or spray foam. Flash exterior surfaces as needed.
• Install a fan that meets Rater-measured airflow codes and standards for local exhaust; meet whole-house ventilation requirements if the kitchen fan is used for whole-house mechanical ventilation. 

See the Compliance Tab for links to related codes and standards and voluntary federal energy-efficiency program requirements.

Description Description

Regardless of what kind of ventilation system you have for the rest of the house, an exhaust fan should be installed in the kitchen to provide point or local exhaust to remove moisture and odors associated with cooking. The exhaust fan is typically located directly over the kitchen stove and is installed in a range hood or cabinet, integrated with a microwave oven, or mounted on the wall. The fan should be ducted to exhaust outside of the home, not into the attic, crawlspace, or another area inside the building. The duct serving the range hood should be made of rigid metal such as galvanized steel, stainless steel, or copper and have a smooth interior surface. It should meet the maximum length guidelines specified in the IRC ( IRC Table M.2) and the minimum diameter guidelines specified in the fan’s installation instructions; small-diameter ducts could trap grease, creating a fire hazard. It should be airtight, equipped with a back-draft damper, and independent of all other exhaust systems. 

Recirculating fans that draw air through a filter and discharge it back into the room are not acceptable. Operable windows are a nice feature but they should not be relied on for consistent ventilation.

Kitchen fans can be run intermittently (occupant controlled) or continuously; some fan models have multiple speed settings and can be used for either.To fulfill the local exhaust airflow requirements of the International Residential Code (IRC ), kitchen fans operated intermittently should have a flow rate of 100 cfm or more and fans operated continuously should have a flow rate of 25 cfm or more. Select fans that are ENERGY STAR rated, and have low sound ratings and low power draw. ENERGY STAR recommends that local kitchen exhaust fans provide ≥ 5 air changes per hour of ventilation, depending on the kitchen volume. ENERGY STAR also recommends that exhaust fans have sound ratings of ≤ 1 sone if set to run continuously or ≤ 3 sones if operating intermittently.

Some home owners are installing commercial-scale cooking ranges with very powerful exhaust hood fans rated as high as cfm. Exhaust fan rates this high can easily backdraft a non-sealed-combustion furnace, water heater, or fireplace (Holladay ). Any installed exhaust fan operating in excess of 400 cfm must be provided with a makeup air system that will automatically start and operate simultaneously with the exhaust fan and will provide makeup air at a rate equivalent to the exhaust fan rate.

Although a single-point exhaust fan such as a kitchen fan could be used to provide code-required whole-house ventilation, this strategy is not recommended. For more on whole house ventilation strategies and requirements, see the Building America Solution Center Guide Whole-House Ventilation Strategies for New Homes and Whole-House Ventilation Strategies for Existing Homes.

Kitchen exhaust fans may be installed by the HVAC vendor or installer or by the kitchen range vendor if it is part of that system. This task should be included in the contract for the appropriate trade depending on the workflow at specific job sites.

How to Install Exhaust Fans

1. Determine the appropriate fan size for your application. For a continuous rate of ≥ 5 ACH, ENERGY STAR recommends selecting a fan that provides more than 5 ACH in order to pull the required amount of air. For an intermittent rate of ≥ 100 cfm, ENERGY STAR recommends selecting a fan with a rating of 150  to 200 cfm. Choose ENERGY STAR-rated fans for energy efficiency and low noise level.

2. Install the fan either in the range hood, the cabinet above the stove, or on the wall above the stove. Follow the manufacturer’s instructions. The fan may also be purchased as an integrated unit that comes with a microwave oven mounted into a cabinet above the stove. Cut openings in the ceiling for the fan or exhaust duct no wider than needed to fit the fan or duct and air seal the opening with caulk or spray foam. Connect the exhaust duct to the fan box with mechanical fasteners and seal with metal tape and/or mastic. Do not use cloth-backed duct tape.
3. Vent the kitchen fan exhaust directly to the outside, not into an attic, crawlspace, or space between floors. Use correctly sized, smooth metal duct. Seal seams and joints with mastic and/or metal tape. Install a back-draft damper that closes when the fan is not in operation. Install the duct with as few bends as possible and out of the way of other ducts or equipment in the attic. Take care not to dent or crush the duct during or after installation. The duct should be independent of other exhaust systems.
4. Locate the exhaust duct outlet vent on the exterior of the home at least 10 feet from any air inlet. The outside termination should be covered with louvers, a screen, or a grille. The exhaust air should not be directed onto a walkway.
5. If the fan is integrated with a microwave oven installed over the stove, install it according to the manufacturers’ instructions and IRC Section M.
6. Exhaust hoods installed over domestic open-top broiler units should be made of metal and have a 1/4-inch clearance between the hood and the underside of combustible material or cabinets. The hood should extend the full width and depth of the cooktop, discharge to the outside, and have a backdraft damper, as specified in  IRC Section M.
7. The exhaust fan flow rate should be tested by a certified energy rater using test procedures listed in ANSI/RESNET/ICC 380-.

Success Ensuring Success

Visually inspect and test the kitchen exhaust fan for proper installation as follows:

• Ensure that the fan exhausts outside, not into the attic; that it is set to exhaust, not recirculate; that any dampers on the outside termination are able to open freely; and that packing tape is removed.
• Confirm that any openings cut in the ceiling for the fan or exhaust duct are properly air sealed and that the exhaust duct is sealed to the fan box with both mechanical fasteners and mastic and/or metal tape and caulk or spray foam.
• Check the sone rating; ASHRAE 62.2- requires 3 sones or less for intermittent (occupant-controlled) kitchen or bath exhaust fans or 1.0 sone or less for continuous fans.
• See the Compliance tab for code and ENERGY STAR guidelines regarding flow rates and efficacy for fans used for local exhaust. See the guide Whole Building Ventilation for codes and standards related to exhaust fans used for whole-house ventilation.
• A certified energy rater will test the fan’s operation to determine the flow rate using a flow hood, flow grid, anemometer, in accordance with test procedures listed in ANSI/RESNET/ICC 380-, or established by the Associated Air Barrier Council, National Environmental Balancing Bureau, or ASHRAE), or other equivalent method. Kitchen fans are typically rated by how many cubic feet per minute the fan will exhaust in a factory setting. Duct work, termination choices, and installation may decrease the measured cubic feet per minute below the factory-rated value.

Climate Climate

No climate-specific information applies.

Training Right and Wrong Images Videos Description Video describing how to properly install a retrofit bath fan. Description Video describing how to properly install a retrofit vent cap. Compliance Retrofit Existing Homes

SCOPE

Install or replace the kitchen exhaust fan, if the kitchen currently lacks an exhaust fan or the existing fan is a recirculating model or has insufficient draw, as determined by occupant experience or through fan testing by a home energy rater.

If the current kitchen fan exhausts into the attic, crawlspace, or between floors, replace the duct with one that exhausts to the outside.

See the assessment guide, Pre-Retrofit Assessment of Attics, Ceilings, and Roofs.

For more on exhaust fan ventilation, see the U.S. Department of Energy’s Standard Work Specifications.

See the Scope tab for additional job specifications.

DESCRIPTION

Installation of a new kitchen exhaust fan is warranted if the kitchen currently has no exhaust fan or if the existing fan is a recirculating model that does not vent to the outside. Other reasons to replace the fan include noise or moisture complaints by the homeowner or fan testing as part of a home energy audit that reveals that the fan has insufficient draw. A less common reason to replace the fan is if it has too much draw. Commercial-grade cook tops that are installed in some home kitchen remodels often come with overly powerful exhaust hood fans that have exhaust flow rates far above what is required by code. If testing by a home energy rater reveals that the exhaust fan is, or could potentially, backdraft the fireplace or other combustion appliances in the home, and it is difficult to find wall space to install a vent large enough to supply a sufficient amount of makeup air to the kitchen, a less expensive option may be to replace the exhaust fan within the range hood with a fan that exhausts at a rate closer to what is required by code. Follow the installation instructions provided in the Description tab.

COMPLIANCE 

See Compliance tab. 

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