How to Choose a Bathroom Exhaust Fan

Bathroom exhaust fans maintain indoor air quality and prevent moisture-related issues. In the video above, This Old House expert Heath Eastman demonstrates various exhaust fan options, features, and installation methods.

This guide describes essential factors to consider when selecting the right bathroom exhaust fan for your home.

Types of Bathroom Exhaust Fans

The most common bathroom exhaust fans include:

• Ceiling-mounted fans: These are the most common and are installed directly in the bathroom ceiling.
• Combination fans: This fan type combines an exhaust fan with other features like lighting or heating.
• Inline fans: These fans are mounted in the attic or another remote location and connected to the bathroom via ductwork.
• Wall-mounted fans: These fans are ideal for bathrooms without attic access or where ceiling installation is not feasible.

Choosing the Right Size Exhaust Fan

A fan’s capacity is measured in cubic feet per minute (CFM), which indicates how much air the fan can move in one minute. To determine the right CFM for your bathroom, follow these guidelines:

1. Measure your bathroom’s cubic footage by multiplying the room’s length, width, and height.
2. For bathrooms up to 100 square feet, you will need 1 CFM per cubic foot.
3. For larger bathrooms, add 50 CFM for each toilet, shower, or bathtub and 100 CFM for a whirlpool tub.

Bathroom Exhaust Fan Noise Levels and Sones

The noise level of an exhaust fan is measured in sones. Lower sone ratings indicate quieter operation. For a peaceful bathroom environment, consider these guidelines:

• 1. 0 sones or less: Very quiet, ideal for master bathrooms
• 1. 0 to 2. 0 sones: Quiet, suitable for guest bathrooms
• 2. 0 to 4. 0 sones: Moderate, acceptable for most applications
• 4. 0 sones or higher: Loud, may be disruptive

Bathroom Venting Considerations

Eastman emphasizes the importance of venting to the outdoors and avoiding common mistakes. When installing a bathroom exhaust fan, consider these best practices:

1. Always vent to the outdoors, never into an attic or soffit.
2. Install a roof cap or wall cap to prevent backdrafts and keep pests out.
3. Minimize the number of bends in the ductwork to improve airflow.
4. Use insulated flexible ducting to prevent condensation and reduce noise.

Eastman recommends venting out a side wall whenever possible. If that’s not an option, venting through the roof is acceptable. However, he strongly advises against venting into an attic or through a soffit, as this can lead to moisture problems and potential mold growth.

Remote Motor Options

For bathrooms where standard venting is challenging, Eastman showcases a remote motor option. This system allows for greater flexibility in installation, as the motor can be located in an attic or basement and connected to the bathroom via ductwork. This option is particularly useful for:

• Bathrooms located far from exterior walls
• Reducing noise in the bathroom itself
• Situations requiring longer duct runs

Energy Efficiency and Additional Fan Features

Some modern exhaust fans come equipped with humidity sensors that automatically turn the fan on when moisture levels rise and off when they return to normal. This feature ensures proper ventilation without relying on manual operation.

Integrated Lighting and Heating

Many exhaust fans now include built-in lighting or heating elements, offering additional functionality in a single unit. These combination units can save space and provide a sleek, integrated look in your bathroom.

Timer Switches

Timer switches are an excellent option for ensuring the fan runs long enough to remove excess moisture. Heath shows two types of timer switches:

1. Mechanical wind-up timer: A simple, reliable option that allows you to set the fan to run for a specific duration.
2. Digital timer: Offers more precise control, typically with preset time intervals.

Advanced Control Modules

For the most flexible control options, Heath presents a modular fan system that allows for various control methods:

• Constant low-speed operation with boost mode during high humidity
• Customizable settings to suit your specific needs
• Plug-and-play modules for different functions (timer, humidity sensor, motion detection)

Expert assistance with this segment was provided by Eaton and Eastman Electric.