But did you know that the steam and humidity that come along with those showers could be wreaking havoc on your air quality? It's true—unless, of course, you're using a bathroom fan. Exhaust fans (bathroom fans) are in-wall or in-ceiling exhaust fans designed to add ventilation, improve airflow, and reduce excess humidity. Technically, these systems remove warm moisture from your bathroom and exhaust it outdoors through your home's ductwork. Using a fan helps prevent mold and mildew problems, maintain healthier indoor air quality, and keeps you safe and comfortable. Here are five things to consider as you shop for a bath fan.

1. Bathroom Fan Sizing

Selecting the right size fan for your bathroom's square footage ensures that you'll get the right amount of ventilation in the space. Bathroom exhaust fans are sized and rated by their ability to move air in cubic feet per minute, or CFMs. Smaller, less powerful fans generate fewer CFMs and are ideal for smaller bathrooms. Bath fans that generate higher CFMs work better in larger bathrooms.

The Home Ventilating Institute (HVI)—an organization that certifies the performance and efficiency of home ventilation products—recommends this guideline for sizing a bathroom fan. If your bathroom measures eight-foot by five-foot with a standard eight-foot ceiling, perform the following formula to find the right CFM.

Example: 320 cubic feet x 8 air changes per hour = 2,560

2,560 / 60 minutes =  42 CFM

The Home Ventilating Institute also recommends adding 50 CFM to every toilet and every toilet and shower or bath combination.

2. Bathroom Fan Installation

Most bathroom fans are installed in a ceiling, but certain models can also be installed in a wall. Units include integrated duct adapters that connect to your home's ductwork. You should install your fan to vent air outside of your home through your ductwork and the nearest soffit, not into an attic. Venting air into an attic only transfers warm, moist air to another area of your home where moisture problems can still develop. When selecting a bathroom fan, first, consider where you want the unit to be installed: ceiling or wall. Then, choose a model with the appropriate size duct adapter (measured in inches) for your home.

Other tips:

• Existing Wiring: Consider installing a fan with light over an existing light fixture for easier wiring and convenience.
• Safety Ratings for Shower + Tub Fans: If you're installing the fan over a shower/tub combo, make sure it's safety certified for this location (typically, UL-listed).
• Professional Installation: For safety, consider hiring an HVAC technician to install your fan and/or an electrician to perform wiring requirements if you need assistance.

3. Features

Today's bathroom ventilation fans have several features that help make operating them more convenient and efficient.

• Integrated Lighting: Many models feature integrated lights that can replace existing fixtures or add supplementary lighting. Some units even include night lights for soft illumination during the nighttime hours.
• Heaters: Fans with built-in heaters help add extra warmth if you live in a cold climate.
• Humidity+ Motion Sensors: Humidity and motion sensors improve the overall efficiency of the fan and help conserve energy. A humidity sensor monitors your bathroom and triggers the fan to turn on when humidity rises above a certain level and then turn off when humidity is reduced. A motion sensor detects when someone enters the bathroom and turns on the fan or light only.
• Controls: Fans with multiple functions usually include separate controls for each function, or you have the option to use them all together. You'll also receive a separate wall switch for convenient control of these functions.

4. Noise Level

Bathroom fans that sound like jet engines can really detract from the peaceful escape that is your bathroom. As you shop for a fan, you'll probably want to consider noise level and choose a quieter model. Bath fan sound is rated in sones. A sone is a measurement of sound as it relates to how it is sensed by the average listener. One sone is equal roughly to the quiet hum of a refrigerator in a quiet kitchen. Two sones would double that sound, and so on. If you're looking for a quiet bathroom fan, choose a model with a sone rating of two and under. Fans rated at three and four sones generate more white noise. Steer clear of fans rated at five or more sones.

5.Efficiency

Efficiency is top of mind when you shop for any home appliance or system. Fortunately, exhaust fans have become more efficient than ever. Energy Star bathroom fans, in particular, use 70% (yes, 70!) less energy than conventional non-Energy Star models. This certainly contributes to low energy costs. They must also meet qualifications for low sound emission, low wattage consumption, and powerful but efficient performance under static pressure.

Choose an Energy Star bathroom exhaust fan to get the most bang for your energy bucks. You might also invest in a fan that includes a motion and/or humidity sensor to help ensure it runs only when needed.

In Summary...

When buying a bathroom fan, first you'll want to consider the size of your space and then additional features such as lighting, heat, and sensors that automatically activate the fan. Lastly, since there can be wide variations, consider the level of sound tolerable for you.