Mechanical ventilation systems are installed in new build and refurbished houses and flats where natural ventilation is insufficient to supply fresh air, and remove indoor pollutants and excess moisture.

The most energy efficient system is mechanical ventilation with heat recovery (MVHR). Heat from the warm air that is being extracted is passed to the incoming fresh air through a heat exchanger. MVHR minimises heat loss, reducing heating costs.

Mechanical extract ventilation (MEV) is similar but doesn't make use of a heat exchanger.

Positive displacement ventilation (PDV), also known as positive input ventilation, circulates the warm air that builds up in loft spaces. This displaces stale, moisture-laden air, which leaves through normal air leakage points.

Most mechanical systems are centralised whole house systems, but single room systems, such as decentralised sill ventilators, are also available.

For ventilating kitchens, bathrooms and utility rooms, extractor fans are commonly used.