How to Choose a New Bathroom Fan

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Broan™ ventilation fans allow your home to exhale, eliminating humidity, odor and airborne particulates from your bathrooms, closets, mud room, laundry, work out space and more. Ventilation fans improve indoor air quality by venting moist air quickly outside, which helps to control mold and mildew growth. Ventilation fans in the bathroom quickly clear steamy mirrors and create a comfortable environment for starting and ending the day. Without properly installed ventilation, rooms with high humidity can experience paint or wallpaper peeling, or costly damage to drywall and wood structures.

Choose the right CFM power level

Make sure you choose a ventilation fan that is powerful enough to clear the air from the room. Use the room size to determine the necessary cubic feet per minute (CFM) power rating of the fan. The CFM power rating measures the volume of air the fan moves. A fan that's too small will not have enough power to remove moisture and odors efficiently and will need to run longer, increasing wear on the motor. To choose the right fan for your room size, use the guidelines set by the Home Ventilating Institute:

For rooms with 8-foot ceilings:

  • A 50-square foot or smaller room needs a 50 CFM ventilation fan
  • For rooms between 50 and 100 square feet, estimate approximately 1 CFM per square foot
  • If your room is larger than 100 square feet, tally the CFM requirements for the individual fixtures to estimate your needs. For bathroom applications, plan for 50 CFM for each toilet, tub or shower and 100 CFM for a jetted tub or whirlpool
  • If your bathroom has an enclosed toilet area, use a separate fan
  • Regardless of the room size, a long run of ductwork connecting the fan to the outside increases the CFM power requirement, particularly if there are bends in the run. No matter the installation, every fan must exhaust to the outside. Exhausting to the attic or between floors does not effectively remove moisture from your home, and could result in costly damage.

Some fans are designed to run continuously. In this case, you'll want at least a 20 cfm rating whatever the size of the room. Because it runs continuously, the fan does not need to be as powerful as one used periodically. Look for a sone rating of 1 or less: if it's on all the time, you definitely want it to be quiet.

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Choose the Right Sound Level

Think about how you will use your room. Is it important that there is still enough sound to know it’s turned on? Or should it be inaudible? Homeowners often mention that they prefer to have a sound level that allows for privacy while the room in in use, particularly a powder room or bathrooms that are in close proximity to gathering areas.

The industry standard for measuring the amount of sound a fan makes when it’s in use is called sones. The lower the sone rating, the quieter the fan will be. Sone levels in the range  of 1.0 to 1.5 are considered just right quiet – enough sound to know the ventilation fan is turned on. Sound levels of less than .3 sones are inaudible to the human ear.

For any room, choose your preferred level of quiet

  • Greater than 2.0 sones, privacy mode, masking level sound
  • Between 1.5 and 2.0 sones, white noise
  • Between 1.0 and 1.5 sones, just right quiet, enough to know it’s turned on
  • Between 0.3 and 1.0 sones, whisper quiet
  • Less than 0.3 sone, inaudible

Many people believe that in order to maximize comfort, an inaudible fan is the best choice. Often, however, they realize that their fan has been running for prolonged periods of time because they weren’t aware the fan was on. In this instance, a humidity sensing fan would complement the inaudible sound, since it automatically turns on and off with humidity changes.

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Choose Energy Efficient

Bathroom ventilation fans that earn an ENERGY STAR label for efficient operation must be independently certified by the Home Ventilating Institute or the Air Movement and Control Association. The standards apply to any lighting options, too. ENERGY STAR ventilation fans use about 60 percent less energy than standard fans.

In some states, bathroom ventilation fans are required to meet building codes. In California, for example, Title 24 sets guidelines for the overall energy efficiency of new homes and additions. Bathroom ventilation fans are part of the HVAC systems that must be evaluated for energy efficiency under Title 24 before building permits can be issued.

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Choose the Right Installation Package

Once you've found the right unit for your bathroom, all that's left is installation. This is a task that's probably best left to professionals, unless you're a seasoned DIYer with electrical skills. Whoever installs it, you'll want to be sure that:

  • the fan is placed in a good location (usually over or near fixtures, or the center of the ceiling, away from openings)
  • controls are effective and convenient (unless using a delay-timer, it's best to have separate switches for lights and fans since it's recommended they run for 20 minutes after a shower)
  • it's vented outside the home (never to an attic or elsewhere)
  • a wall or roof vent cap is also installed to keep your home sealed when the fan isn't in use

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.


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. 

Some models of bathroom fans include built-in heaters to improve warm air circulation or humidity sensors that automatically turn on the fan when it's needed most.

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 duct diameter to the new fan.

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More Tips & Tricks

Always Vent to the Outside.
Bathroom ventilation fans often are set up so that they exhaust air to the space between ceiling joists, especially if the bath is located on a lower level toward the middle of the house. Venting to the space between joists or into an unheated attic vents excess moisture into the worst possible conditions—closed, dark spaces where humidity condenses on cold surfaces and mold can spread, damaging floors, walls and ceiling materials.

A smarter, healthier alternative is to connect your bathroom exhaust fan to vent ducts that channel the exhaust outside your home. Building codes typically specify this solution; regardless, it's the most sensible and safest method.

Consider Exchange Ventilation.
Keep in mind that properly vented ventilation fans also suck a lot of heated air out of your house. A remedy is to install a heat-exchange ventilator fan. These fans use warm, outgoing air to heat cooler, incoming replacement air. Heat exchanger models sell for about twice as much as standard bathroom ventilation fans.

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