Mechanical Ventilation with Heat Recovery (MVHR)

About this course.

Mechanical ventilation with heat recovery (MVHR) is a whole-of-home ventilation system that continuously supplies filtered fresh air to living and sleeping rooms and continuously extracts stale, moist air from kitchens, bathrooms and laundries, while a heat exchanger recovers most of the energy from the outgoing air and transfers it to the incoming air. In short, it gives an airtight building a steady supply of good, filtered fresh air without throwing away the energy already used to heat or cool the indoor air. Airtight, high-performance homes need it because, once a building is deliberately sealed, it can no longer rely on uncontrolled leakage to ventilate itself — fresh air must be provided on purpose.

To understand why controlled ventilation has become important, it helps to see what has changed in how we build. For comfort, lower energy bills and lower carbon emissions, high-performance homes are built with continuous insulation and a deliberate, continuous air barrier so that air only moves in and out where the design intends. That is a good thing: uncontrolled air leakage wastes energy, causes draughts and uneven temperatures, and can carry moisture into the building fabric where it condenses and causes mould and decay. But sealing a building has a direct consequence — the accidental "ventilation" that older, leaky houses got for free, through gaps around windows, floorboards, downlights and service penetrations, largely disappears. A tight building that is not deliberately ventilated becomes stuffy, humid and unhealthy. The industry shorthand captures the whole idea: "build tight, ventilate right."