Ducts are used in heating, ventilation, and air conditioning (HVAC) to deliver and remove air. These needed airflows include, for example, supply air, return air, and exhaust air. Ducts also deliver, most commonly as part of the supply air, ventilation air. As such, air ducts are one method of ensuring acceptable indoor air quality as well as thermal comfort.
A duct system is often called ductwork. Planning ('laying out'), sizing, optimizing, detailing, and finding the pressure losses through a duct system is called duct design.
Whilst planning ducting a bathroom it is important to know duct size and where you would like to your bathroom fan to vent. Typically, ducting runs towards the attic and out the side. If using flex duct always, always try to keep it straight as possible, as kinks and bends will significantly decrease airflow. Also, ducting will need to be cleaned to prevent mold and dirt build-ups that could affect the quality of air in your home.