Bathroom exhaust vents

As a home inspector sometimes people will ask, “Do I need a bathroom exhaust fan?”  Plain and simple your bathroom needs an exhaust fan to prevent moisture problems.  Taking showers and baths causes moisture to be pumped into the air.  In the winter, this moisture condenses on windows and walls and can make its way into the attic through attic bypasses thus creating frost.


Some states require windows in the bathrooms to provide a total glazed area of at least three-square feet and half must be openable. Exceptions to this rule could be if there is an exhaust fan installed that will exhaust at least 50 cubic per minute. Another option would be a continuous exhaust system such as a heat recovery ventilator that exhausts 20 cubic feet per minute.


Most people will not open a window on a cold winter day to reduce moisture. If your home does not have an exhaust fan in your bathroom, you should consider installing one.


Here are some tips for fan installation:


  1. Be sure to choose a good fan. You will need to balance noise level, performance, and price. A cheap noisy fan is likely not to even be turned on.


  1. Make the exhaust duct short. It should be as short as possible and take as few turns as possible. The longer the duct and the more twists and turns it takes, the less the air flow.  For example, if the bath fan is in the basement and the duct runs up to the roof at the second floor, air flow will be less than stellar.


  1. Be sure to insulate the duct where it passes through unconditioned spaces such as the attic. Otherwise, moisture will condense in the duct and could drop down and stain the ceiling.


  1. Don’t use a standard switch to control the fan. A single switch control doesn’t usually run long enough to remove enough moisture. Installing a timer which runs for at least a half hour is a better option. Another good choice would be a humidity sensing switch.


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