Central mechanical ventilation units extract stale, moist air from wet rooms and some also supply fresh, clean air to habitable rooms. To do this they need a ductwork system with the following components:
- Roof and/or wall terminals, which penetrate the building fabric
- Air-tight seals for the terminals in warm loft spaces to keep the building fabric air-tight
- Often insulated mass flow ductwork between the terminals and the ventilation unit to minimise the risk of condensation
- Sound attenuators downstream of the ventilation unit to minimise noise hindrance
- Ductwork systems between the ventilation unit and rooms to distribute air to and from them
- Supply and/or extract valves in the rooms
