Fresh-air ventilation explained: filtered air without opening a window

Why homes need fresh air

Cooking, showers, drying clothes and simply breathing all add moisture and stale air to a home. Older, draughty homes swap air through gaps whether you like it or not. Newer homes are built much tighter to save energy, which is great for bills, but it means fresh air has to be planned in rather than leaking in.

How heat recovery works

• One small fan draws stale air out of wet and busy rooms: kitchen, bathrooms, laundry.
• Another brings outdoor air in through a filter that catches dust and pollen.
• The two airflows pass each other, without mixing, through a heat exchanger. In winter the outgoing warm air warms the incoming fresh air; in summer it works the other way.
• Ducts deliver the fresh air to bedrooms and living areas. It runs all the time at a low, quiet speed, with a boost for cooking or showers.

When it's worth it

• New builds and major renovations, when ducts are easy to run.
• Well-sealed homes, where condensation or stuffy rooms are a sign that air isn't changing enough.
• Homes near busy roads, or where you'd rather keep windows closed for noise, pollen or smoke.
• Less worth it in a very draughty older home: sealing the gaps comes first, or the system has to work against them.

What it takes to run

• The fans are small and use a modest amount of power, running around the clock. With solar, the daytime running is on your own sunshine.
• Filters need cleaning or changing, usually every few months to a year, depending on the model and how dusty it is outside.
• Installation needs ceiling space for the unit and ducts, and a qualified technician to set up and balance the airflows.

Revo's tipBefore any system, try the free version: run the bathroom and rangehood fans while you shower and cook, and leave them on for ten minutes after.

Take the Home Health check