These photos were taken of a fan that has a 6 week cleaning frequency, it would be really dirty if it had a typical 3 month schedule . Hood cleaning frequency varies depending on the restaurant . It important to have a correct cleaning frequency. Frequencies can range from six weeks the 3 months to 6 months to one year for a restaurant that has low volume. A single kitchen may have several hoods, all with different cleaning schedules. We are happy to find the right schedule for you.