067: How to buy a bathroom exhaust fan

Bathroom fan is one of the most essential home appliances and used to exhaust the moisture, unpleasant odours and moulds in bathrooms.

To choose a right bathroom fan first you must calculate the ventilation as below:

1- Calculate the area of the bathroom: Length multiplied by width (S= L x W) - based on square feet

2- Calculate the CFM (Cubic Feet per Minute) rating: It means how much air must be circulated by fan (the maximum airflow)

How to calculate the CFM?

1- For bathroom up to 100 square foot: 1 CFM for each square foot.

2- For bathroom more than 100 square foot:

• 50 CFM for each toilet
• 50 CFM for each shower
• 50 CFM for each bathtub
• 100 CFM for each jacuzzi

3- Check the static pressure

Note1: Static pressure is the airflow resistance through the ventilation duct and reduce the output of the fan. Static pressure depend on below items:

• Duct length
• Duct diameter
• Number of the elbow

4- Measure the noise rating: Measure the loudness of noise caused by fan while rotating.

• noise rating under 1:  Very quiet
• noise rating between 1.5-2: Acceptable
• noise rating over 4: Noisy and not acceptable

5- Selection the optional features for the fan:

• Humidity sensor
• Motion sensor
• Timer delay
• Light
• Heater
• Speaker

6- Select the installation material:

• Duct/Pipe
• Connections
• Air grille / Ventilation grille
• Wall switch or fan controller

Some examples:

• Small sized bathroom with 50 square foot, needs 50 CFM fan.
• Medium sized bathroom with 100 square foot, needs 100 CFM fan.
• Large sized bathroom (master) with one shower booth (stall), one toilet and one bathtub, needs 150 CFM fan.

Note2:

• 1 cfm = 1.699 cubic meter per hour (m3/h)
• 1 cubic meter per hour (m3/h) = 0.589 cfm
• for example if you buy one fan in Europe with 100 m3/h its approximately equal to a 58.9 cfm fan (100 x 0.589)