It Depends. attic fans come in a variety of sizes, so it's important to know the size of your fan in order to answer this question accurately. In general, you should run your attic fan for as long as possible during the hot summer months. However, if your attic is already cool, you may not need to run your fan as often.

The general rule of thumb is to have the fan running for as long as the temperature difference between the inside and outside of your home is 20 degrees or more. So, if it's 75 degrees Fahrenheit outside, you'd want the fan to be running so that the temperature inside your home is no more than 55 degrees. If it's 95 degrees outside, you'd want the inside of your house to be no more than 75 degrees.