Larger bathrooms may have additional fixtures, especially jetted tubs or both a shower and bathtub, which produce more moisture and increase the need for ventilation. The Heating Ventilating Institute recommends that for larger bathrooms (over 100 square feet) (9.3 square meters), determine ventilation based on the fixtures. Add fan capacity as follows:
• Toilet: 50 cfm (23.6 liters per second)
• Shower: 50 cfm (23.6 liters per second)
• Bathtub: 50 cfm (23.6 liters per second)
• Jetted tub: 100 cfm ( 50 liters per second)
Fan controls
Bathroom fans are available with different types of control systems. Whatever types of switches are chosen, make sure that they are easy to read and understand, and that clients can operate them.
Sensor controls are available that turn fans on and off based on humidity, and can provide excellent moisture control. Motion detectors turn a fan on when someone is in the bathroom, and then turn it off after they leave. However, motion detectors may not work effectively in some situations, such as when someone is soaking in a tub. Automatic timers can be convenient.
After showering or bathing, it may take time for moisture removal from the bathroom and ventilation system. The Home Ventilating Institute recommends that the ventilation system continues to operate for 20 minutes after use of the bathroom. A timer switch can help provide moisture control without wasting energy. Electronic timers can be easy to use, accurate, and offer many features. Variable speed controls allow the user to match the speed of the fan to the need for ventilation. The ability to run the fan at a slower (and quieter) speed may encourage more frequent use of ventilation.
Some fans are wired into the same switch as the bathroom light, so that the fan comes on with the light. This is a good way to ensure that ventilation is always provided. If this type of switching is selected, it is very important to use a quiet fan. Putting the light and fan on the same switch does have a drawback. To leave the fan running after bathing or showering, the light must also be left on—even if no one is in the bathroom.
Fan Location
Warm air tends to rise. In addition, the warmer the air, the more moisture it holds. Therefore, the warmest air, with the most moisture, tends to be near the ceiling. So the ceiling, or a high place on a wall, is the best place for a fan.
Another factor in fan location is having the air intake close to the source of air and moisture to be exhausted. Therefore, the best location for the fan is usually near the toilet, bathtub, and/or shower. Some fans are designed to be located in the shower or directly over a jetted tub. They are usually described as "vapor proof" or "moisture proof."
Consider the visual impact of the fan in placing it. The color and style of the fan grille, the choice of materials, and the relationship of the fan to other features such as lights that are mounted on the ceiling and wall should all be considered. In a larger bathroom, you may want to specify two exhaust fans, one over the toilet or near the floor, and one over the bathtub or shower. The size of these two fans can be added together to determine the total ventilation capacity of the bathroom. An advantage of using two smaller fans is that the smaller fans are usually quieter than one larger fan, which might encourage their use.
If the toilet is in a separate compartment, it will need its own ventilation fan. This can be sized using the eight ACH formula.
The relationship of the interior air intake (in the bathroom) and the exterior air exhaust (outside) needs to be considered in locating the fan. Minimizing the length of the duct run, as well as the number of elbows or bends, will increase the efficiency of the fan system.
