FEMA.gov recommends cleaning your dryer vent once annually, but it can depend on many variables. The number of people in the house causes the use of the dryer to go up. The length of the dryer vent pipe can factor into the amount of air being pushed from the dryer and will lose velocity and cause more lint to settle in the dryer vent. Anything over 30 feet can stress the dryer motor. A good rule of thumb is to not wait longer than 2 years for any size house or family.