Today's homes and buildings are much more airtight than older ones. That is good for energy, but the indoor air is not renewed: humidity, odours and carbon dioxide build up, and mould appears. Opening windows fixes the air, but throws away the heat in winter and the cool in summer.
A heat recovery unit, or mechanical ventilation with heat recovery (MVHR), renews the air continuously and in a controlled way, recovering the heat from the outgoing air.
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The two airflows cross in thin plates, exchanging heat without mixing. It has filters and fans.
Enters filtered and cold. Passing through the exchanger it picks up heat from the outgoing air.
The kitchen and WC extract moisture and odours. This is where the home's heat gets recovered.
Supplied to the lounge and bedrooms already close to room temperature, with no cold draughts.
Leaves for the outside after giving its heat to the fresh air.
The two airstreams pass through the heat exchanger in separate channels: they never mix, so the odours and humidity from the kitchen and toilet do not return to the bedrooms. According to the manufacturers, the best models recover most of the heat, in the order of 75 to 90%.
Two ways to install
| Centralised | Decentralised | |
|---|---|---|
| What it is | One unit with ducts to every room | Small wall-mounted units, one per room or per pair of rooms |
| Best for | New builds and major refurbishments | Existing buildings with no space for ducts |
| Work required | Ducts in the ceiling or loft | Holes in the wall, no ducts |
Residential and commercial
| Residential | Commercial | |
|---|---|---|
| Problem it solves | Damp, mould and stale air in bedrooms | Fresh air in rooms with many people, such as offices, meeting rooms and shops |
| Link with air conditioning | The fresh air arrives already tempered: the air conditioning works less | Reduces the thermal load that the air conditioning has to overcome |
In a humid climate
In the Azores, damp is a frequent complaint. Ventilating well is the most effective way to control it, and doing so with a heat recovery unit avoids the discomfort of cold air coming in.
Maintenance
The filters must be replaced or cleaned regularly, and the heat exchanger checked from time to time. It is simple maintenance, but without it the equipment loses efficiency.
Is it noisy?
Well-sized, well-installed models are quiet. Noise depends on the airflow and the quality of the installation.
Can I install one in an existing home?
Yes. If there is no space for ducts, there are decentralised solutions, fitted directly into the wall.