Find the Best Bathroom Exhaust Fan for Your Home

Make sure the fan you choose is powerful enough to ventilate your bathroom. The room’s size determines the necessary cubic feet per minute (CFM) rating of the fan. The CFM rating measures the volume of air the fan moves. As a general rule, you’ll need at least 1 CFM per square foot of space. A fan that’s too small won’t remove moisture and odors efficiently and will need to run longer, increasing wear on the motor. The following guidelines can help you find the right fan for rooms with 8-foot ceilings.

• A bathroom 50 square feet or smaller needs a 50-CFM fan.
• For bathrooms between 50 and 100 square feet, estimate approximately 1 CFM per square foot.
• If your bathroom is larger than 100 square feet, tally the CFM requirements for the individual fixtures to estimate your needs. Plan for 50 CFM for each toilet, tub and shower and add 100 CFM for a jetted tub.
• If your bathroom is smaller than 50 square feet, a 50-CFM fan will work.
• Regardless of the room size, a long run of duct work connecting the fan to the outside increases the CFM requirements, particularly if there are bends in the run.

Note that if your bathroom has an enclosed toilet area, the space needs its own fan.

While the fan’s CFM should be rated for the square footage of the room, it’s a good idea to size the fan up a little. For example, get a 70-CFM fan for a room that’s 65 square feet.

When considering a new or replacement bathroom exhaust fan, always check the sone rating. Sones are measurements of sound. They aren’t measured in specific decibels or volume levels, but they’re an indication of the comparative comfort level of someone who hears the sound. Sones are an important consideration for your bathroom exhaust fan because they give you a relative idea of how loud the bathroom noise will seem. They’re a good indicator of whether you’ll be satisfied with the fan’s noise level. A lower sone rating means a quieter fan.

A bathroom exhaust fan with a sone rating of 1 or lower is quiet and discreet and is usually the preferred sound level for most people. However, bathroom exhaust fans with higher sones are available.

To give you an idea of how loud a sone is, here are some noise-level comparisons for different sone ratings.

• A 1-sone rating is comparable to the hum of a refrigerator.
• A 2-sone rating is comparable to a quiet office.
• A 3-sone rating is comparable to a normal conversation.
• A 4-sone rating is comparable to the noise of a TV or radio.
• A 5-sone rating is comparable to a busy restaurant.

If you’re replacing a fan, take note of the dimensions of the cutout for your existing fan so you can buy one that fits. Here are some other considerations when purchasing a bathroom exhaust fan:

• Ceiling-mount bathroom exhaust fans are the most common models. They connect to an exhaust duct that runs through the attic or between floors. Wall-mount bathroom exhaust fans are designed for rooms where venting through the ceiling isn’t practical. These fans typically vent directly through the wall to the outside with little or no exhaust duct work. Some fans will work in either a ceiling- or wall-mount installation.
• Check the size of the exhaust port on the fan to make sure it fits your duct work. A diameter of 4 inches is common for exhaust ducts, but some high-CFM fans fit a 6-inch-diameter duct. You can upgrade to a duct with a larger diameter for greater efficiency, or you can use an adapter/reducer, which is often included with the fan, to fit the smaller duct.
• A bathroom exhaust fan may be listed for installation over bathtubs and showers when it can be connected to a branch circuit that’s protected by a ground fault circuit interrupter.
• Make sure the fan won’t overload the electrical circuit. Larger, more powerful motors on high-CFM fans draw more power. Features, such as lights and heating elements, increase the demand.
• The fan motor and accessories, such as heaters and lights, can create high temperatures. If you’re installing a fan in an insulated ceiling, make sure the fan is appropriate for contact with insulation.

Here are a few things to remember about bathroom exhaust fans.

• Make sure the bathroom fan you choose is ducted properly. Fans should be vented to the outside, not to the attic or crawlspace. If the duct work isn’t accessible through the attic, vent the fan through an outside wall of the house.
• Be sure the fan is vented with the right size duct.
• Let the exhaust fan run for 20 minutes after someone showers to ensure the proper amount of ventilation.
• Consider a bathroom exhaust fan with a humidity sensor because it’s convenient and responds to changes in humidity to activate the fan automatically.
• Purchase a bathroom exhaust fan with a motion sensor if you’d like it to turn on when you enter the bathroom. Many also have a low sone rating.

If you plan to install your own bathroom exhaust fan, our guide to Installing a Bathroom Exhaust Fan can help. If you need to install a whole house fan, we can help with that, too. If you plan to refresh or renovate your entire bathroom and need help with bathroom installation, we’ve got you covered.