Bathroom vent fans are a very important, yet, often overlooked household appliance. The main purpose of the bathroom fan is to vent the moisture that is created by showering and bathing; removal of odors is also a function. Without a fan to vent the moisture, the moisture stays in the room and can cause mold, mildew and odors. Some of the moisture can permeate the walls and ceilings and cause damage in the wall and ceiling cavities. Have you ever showered without a window open or a vent fan? Try it, return to the bathroom 45 minutes later and you can still feel the moisture in the air; this is humidity.

Some codes do not require a bathroom fan if there is a window in the bathroom that can act as a vent. When I was a teenager, my parents house had a window in the bathhroom, but no fan. I would open the window before I would get in the shower and it worked quite well. Some people do not like to do that in the winter.

I inform my clients that even with a window present, that they should consider installing a bathroom fan. This will help vent the moisture for those days when they do not want to use the window.

So how do you know what capacity fan you should install? The fans are rated based on the amount of air they can move in (CFM)cubic feet per minute. You want to move enough air for 8 air exchanges per hour.

There is a simple formula you can use to determine the CFM of the fan your bathroom requires. First, measure the height, length, and width of the bathroom, this will give you the volume.

Then follow this formula: CFM=Volume/7.5. For example, I have a bathroom that is 7 ft floor to ceiling, 12 feet long, and 5 feet wide. So 7x12x5=420, CFM=420/7.5, CFM=56. I would need a fan that is rated at 56CFM or greater.

Remember, install the fan according to manufacturers instructions. If you are not comfortable installing the fan, please hire a qualified contractor to perform the install.

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