How to Calculate the Size of a Bathroom Fan
- 1). Measure the dimensions of your bathroom in feet. If you are planning a bathroom that has not yet been built, use your blueprint dimensions. Since you will be using volume, not square footage, make sure you measure the height of the ceiling.
- 2). Calculate the volume of the bathroom by multiplying the length, width and height. For example, if the room was 14 feet long, 12 feet wide and 8 feet high, your volume would be 1,344 cubic feet.
- 3). Determine the number of minutes per air change. Most bathrooms are fine, refreshing the air every 7.5 minutes or eight times per hour.
- 4). Divide the volume of the bathroom by the number of minutes per change. For example, a 1,344 cubic foot bathroom divided by 7.5 minutes per change would give you 179.2, which means you would need a fan with a capacity of at least 179.2 CFM.
