How often does my dryer vent need to be cleaned?

This depends on the length of your vent, the angles in your vent, and how much you use your dryer.  A clean vent pipe allows the dryer to move the proper amount of air through the system taking the humidity out of the clothes.  A dirty dryer vent can force your dryer to run longer and harder in order to properly dry your clothes.  This can cause your dryer to overheat igniting the flammable lint in the dryer and vent which can start a house fire.