Also known as a System 3 ventilation system. Air from moist spaces like kitchen, toilets and utility rooms is extracted from this form of ventilation system.
The replacement air is supplied through background ventilators. Alternatively, when the building has a design permeability greater than 5 m3/(h.m2) @ 50 Pa, background ventilators (trickle vents) are not required. The system can either be a centralized system with a single fan connected to various rooms or a decentralised system (dMEV) with air extracted from each room by individual fans. There are two airflow rates, trickle and boost. Air heat pumps for exhaust air would be regarded as a central MEV form.