Which fan for bathroom?

Installing a bathroom exhaust fan is worth the time and effort because it removes hot, moist air and odors. Moist air leads to mold growth and odors lead to general unpleasantness.

But installing a weak, undersized exhaust fan is almost not worth the effort, even if the fan meets the minimum requirements. It's important to understand how vent fans are sized and how to choose one with the proper capacity for your space.

There's a difference between an exhaust fan and ventilation fan; an exhaust fan draws air out and a ventilation fan brings fresh air in. If you have to replace a bathroom exhaust fan, your best bet is to go with the type that's already in place. Four types of bathroom exhaust fans include:

Bathroom vent fans are rated for the amount of air they can move, measured in cubic feet per minute, or CFM. Standard fan sizing applies to bathrooms that are 100 square feet or less. The rule of thumb is that you need at least 1 CFM per square foot of room area.

To determine the square footage of your bathroom, multiply the length times the width. For example, if your bathroom is six feet wide and nine feet long, its square footage is 54. Therefore, it should have a fan rated for at least 54 ​CFM. But before you start shopping, there are a few things to consider.

When sizing a vent fan, a factor to consider is duct size and length. Most 50 CFM fans will run well with a 4-inch round duct. But as you get up into the higher CFM fans, duct size will have to be increased to a 5- or 6-inch round duct. The length of the run, as well as the number of fittings and elbows will also affect the amount of air your duct can effectively carry.

There are somewhat complicated formulas for calculating proper duct size for different length runs and configurations, but the instructions that come with the fan will outline the requirements. Just make sure there is sufficient space for the ductwork in the area where you're installing the fan. Trying to force too much air through an undersized duct will make the fan work too hard and will provide insufficient venting.

For bathrooms over 100 square feet, exhaust fans can be sized according to the number of fixtures in the room. To calculate using this formula, add up the required CFM ratings for all of the fixtures:

For example, if your bathroom includes just a shower and a toilet, it needs a 100 CFM fan, while a bathroom with a jetted tub, toilet, and shower needs a 200 CFM fan.

Another calculation method with three steps is useful for large rooms with high ceilings (well over 8 feet). In this method, multiply the square footage by the ceiling height, divide by 60 (minutes in one hour), then multiply by eight (recommended number of air exchanges per hour). For example, for a room that's 120 square feet and has a 10-foot ceiling:

Once you've chosen the right fan size for your bathroom, consider the sound rating, as demonstrated by the sone rating of each fan. (Sone rating is a measure of loudness.) A quiet fan might be a worthy investment, particularly in a bathroom you'd like to make peaceful and relaxing. The lower the sone number, the quieter the fan will sound when running. A sone rating of "1" is the quietest fan you can buy. Here are other sone ratings compared to other sounds:

If your bathroom has a toilet or shower area enclosed by a door, it's a good idea to install a separate exhaust fan for that area. If the enclosed space is small, a 50 CFM fan should suffice. Otherwise, use the appropriate calculation based on the room size. Just remember that the fan needs airflow to do its job.

Excess moisture has tremendous potential for damaging bathrooms. During a bath or shower, humidity levels rise significantly creating the perfect breeding ground for mold, mildew and microorganisms that can negatively impact health. In addition, long-term exposure to excess moisture and humidity can crack and peel paint and wallpaper, ruin wallboard, warp doors and rust cabinets and fixtures. Without control, it can even cause deterioration of joists and framing above the bathroom.

Most of today's new homes are highly insulated and practically air tight, saving energy but making proper mechanical ventilation essential to maintaining good indoor air quality. Good ventilation protects both your health and your home and is especially important in bathrooms which experience high levels of moisture and humidity.

What is a bathroom exhaust fan? What does it do? A bathroom exhaust fan is a mechanical ventilation device which, when ducted to the exterior of the house, draws out stale, impure and very humid air thereby improving the quality of indoor air.

Why do I need one? A properly installed bathroom exhaust fan will rid the bathroom air of excess moisture, humidity, odors and other pollutants. It also helps to remove water vapor that has accumulated on mirrors and walls. Occupants will be much more comfortable with proper ventilation. In addition to improved indoor air quality, deterioration of the home is minimized saving the homeowner costly repairs.

What do I look for when selecting a bath fan? The proper bathroom exhaust fan should be selected on the basis of performance, style and features.

The correct air movement capacity is an important consideration. Air movement is typically measured in cubic feet per minute (CFM). Ventilation rates based upon eight air changes per hour are generally suggested. For most bathrooms this works out to one CFM per square foot of bathroom area. For example, a 7' x 10' bathroom would require a 70 CFM fan. A 50 CFM rating is recommended as a minimum for bathrooms 50 sq. ft. and smaller. Larger bathrooms require additional ventilation capacity. The following chart can be used as a guide for proper bathroom ventilation.

*Note that these rates represent a minimum requirement. Higher ventilation rates are also acceptable and will have a minimal energy impact.

Other ventilation considerations include:

Noise level is also a consideration when selecting bathroom ventilation. Bathroom fan sound levels are measured in sones: 4.0 sones is the sound of standard television operation; 3.0 sones is typical office noise; 1.0 sones is the sound of a refrigerator; and 0.5 sones is the sound of rustling leaves. For quiet bathroom ventilation the fan should be rated at 1.0 sones or less.

Finally, style and additional features are considerations when selecting the proper bath exhaust fan. There are many attractive options for bath fans to accommodate any budget or décor preference. Additional features may include a light, heating element or a timer or humidistat for automatic operation. Homeowners can easily select bathroom ventilation products that complement the bathroom design while also protecting the bathroom from the perils of moisture.

What else should I consider when purchasing a bathroom exhaust fan? Consumers should always look for the 'HVI-Certified' label. This indicates the unit has gone through rigorous independent performance testing. Most manufacturers offer a wide range of products in different capacities to accommodate the air exchange requirements of the wide variety of bathrooms found in today's homes. A knowledgeable HVAC contractor is recommended for installation.

Why should I choose an 'HVI-Certified' product? In short, peace of mind:

Indoor air quality can be problematic at any time of year, but it is especially a concern during the winter months when all of the windows are sealed up tight…and nowhere is this more evident than in the bathroom. Stale air, humidity, mold, mildew and—to put it delicately—foul odors can wreak havoc with your indoor environment. The solution: install a bathroom exhaust fan.

Bathroom exhaust fans typically come in one of three styles: ceiling-mounted, wall-mounted or inline/remote.

A bathroom exhaust fan is a key component to preventing humidity and moisture buildup, which can damage paint and also lead to the growth of mold and mildew.

The Home Ventilating Institute recommends that every bathroom have an adequate ventilation system that changes the air eight times an hour.

According to HVI, an easy approximation is to provide one cubic foot per minute (CFM) per square foot of bathroom, or a minimum of 50 CFM. So, if your bathroom measures 10 feet by 8 feet, for instance, you have 80 square feet and will want a fan rated for at least 80 CFM.

For bathrooms larger than 100 square feet (10-by-10) The Institute also suggests adding 50 CFM for each toilet, shower and bathtub; and adding 100 CFM for a whirlpool tub.

Once you ascertain the proper air rating, there are several other factors to consider.

Bathroom fan noise levels are measured in sones, with a higher number of sones equating to a louder fan. The HVI recommends fans with a noise level of 1.0 sones or less; there are numerous models available with ratings as low as .03 sones.

Energy efficiency is also a consideration: Energy Star-rated bathroom fans use 20% less energy than minimum federal guidelines. Many bathroom fans also come with an on/off timer, to save electricity; humidity sensors, which cause the fan to turn on only when moisture is present; or motion sensors, which turn the fan off automatically once someone leaves the room.

Features and aesthetics also come into play when choosing a bathroom exhaust fan. In one of our bathrooms, for instance, we installed a fan/light combination with a nightlight option; in another bathroom, we installed a fan/light combination with an accessory heater (which makes it particularly nice to step out of the shower!) There are also various styles from which to choose, including contemporary, traditional and industrial looks.

Installing a bathroom exhaust fan is well within the reach of most do-it-yourselfers, although there are some considerations to take into account before you begin.