When inspecting homes I often come across exhaust fans with a 24 or 12 hour timer installed, serving as a simple ventilation system. Typically, these are located in laundry rooms or bathrooms and many homeowners are unaware of their intended purpose.
The timer can be configured to operate the fan automatically one or more times per day for a set length of time. These fans help reduce moisture and stale air inside the house. Guidelines vary for when and how long such fans should be configured to operate depending on the size of the house, number of occupants and rating of the fan. When found it is recommended to review instructions or documentation for the timer and configuring the fan as necessary. At a minimum, recommend setting the timer for 1-2 15 or 30 minute intervals per day for improved IAQ (indoor air quality).
Washington State Home Inspector #1266
Serving Whatcom, Skagit and Snohomish County