How to Size a Broan Bathroom Exhaust Fan

Broan produces a variety of bathroom exhaust fans with different capacities. They measure this capacity in cubic feet per minute (CFM), that is, how many cubic feet of air moves through the system in a minute. To calculate the minimum capacity that you will need for your bathroom exhaust, according to Broan, you will need to calculate the height and area of your bathroom and multiply it by a factor provided by the manufacturer.

Tape measure

Instructions

- 1
  Measure the dimensions of each side of the room in feet.
- 2
  Calculate the area of the floor using the dimensions. For a rectangular room, you can simply multiply the length by the width of the room. For other shapes, you will need to break the room down into smaller, rectangular shapes and add up the total floor size.
- 3
  Measure the height of the room in feet.
- 4
  Multiply the height of the ceiling by .1375 if the height is greater than 8 feet and multiply the product by the area of the floor to get the recommended cubic feet per minute. For a ceiling that is 8 feet tall, simply multiply the area of the floor by 1.1. In either case, this gives you the manufacturer's minimum recommended CFM figure.

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