How to Size a Bathroom Fan

The size of a bathroom fan is measured in cubic feet per minute. Having a properly sized fan is important because the hot, humid air needs to be cycled out of the room in order to prevent damage to doors and paint, and mold infestation. If your fan is too small, the moist air will remain in the bathroom. To determine the size of the fan, you need to know the volume of your bathroom.

Instructions

- 1
  Measure the dimensions of your bathroom. For a rectangular room, use length, width and height. For a circular room, measure the diameter and divide by 2 to get the radius. Also measure the height.
- 2
  Calculate the volume of your bathroom. For rectangular rooms multiply the length x the width x the height. For circular rooms, multiply the radius x the radius x pi (about 3.14) x the height.
- 3
  Divide the volume by 7.5, which is the number of minutes that it should take the air in the room to be refreshed. For example, if the volume of your room is 1,500 cubic feet, you would need a fan capable of moving 200 cubic feet per minute.

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