Ventilation Installation London: Fans, PIV and MVHR

London flats are small, busy and often sealed tight behind new double glazing. Cooking, showers and drying washing indoors put litres of water into the air every day, and with no way out it condenses on the coldest walls.

More than half of London households live in flats, many with an internal bathroom and no opening window. In those homes a working fan is the only ventilation the room gets.

London at a glance

Homes that are flats: 54.0% of London households (1.8 million) lived in a flat, maisonette or apartment in 2021, against 21.7% across England and Wales. Source
Record heat: St James's Park and Heathrow both reached 40.2°C on 19 July 2022. That night Kenley, in Greater London, set the UK record for the warmest night at 25.8°C. Source
Cooling policy: London Plan Policy SI 4 sets a cooling hierarchy that puts air conditioning last, after shading, insulation and ventilation. Boroughs apply it when they judge applications for outdoor AC units. Source
Local grant: The Warm Homes: Local Grant is run across London by the Greater London Authority for privately owned homes rated EPC D to G, usually with household income of £36,000 or less and savings under £25,000. Source

Fix the fans first

Kitchens and bathrooms have minimum extract rates, set out in Approved Document F. Plenty of London bathrooms have an old fan that moves a fraction of that, or one that blows into a ceiling void instead of outside. Ask the installer to measure the airflow, not just swap the fan.

Humidity-controlled fans keep running until the room has dried, which helps in shared flats where nobody remembers the switch.

PIV and MVHR

Positive input ventilation pushes filtered air in from the loft, or through an outside wall in a flat with no loft, and lowers humidity across the home. It's a common fix for condensation in older conversions.

Mechanical ventilation with heat recovery suits airtight homes: new builds, deep retrofits and large extensions. It needs space for ducts, so plan it during building work rather than after.

Ventilation and heat

The 2022 heatwave kept Kenley at 25.8°C overnight. The London Plan's cooling hierarchy puts ventilation ahead of air conditioning, and a summer bypass or purge mode on MVHR can bring cooler night air in without opening windows to street noise.

London homes and what they need

Converted flats and mansion blocks

In most blocks, leaseholders need the freeholder's permission to core a new vent through an outside wall. Flats also lack the permitted development rights houses have, so ask the borough before cutting a vent in a front wall in a conservation area.

Victorian and Edwardian terraces

Open chimneys and loose sashes used to ventilate these houses. Once fireplaces are blocked and windows replaced, trickle vents or fans have to make up the difference. Fit a vent to any blocked chimney breast to stop damp patches.

Areas covered

Engineers who cover London work across areas including Islington, Hackney, Camden, Brixton, Wimbledon, Ealing, Croydon, Walthamstow, Greenwich and Richmond.

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Questions people in London ask

Can a grant pay for ventilation?

The Greater London Authority lists ventilation and damp prevention among the measures the Warm Homes: Local Grant can fund, for eligible homes rated EPC D to G.

Will a PIV unit make my flat colder?

Most units temper the incoming air with a small heater or draw it from a loft that is warmer than outside. You may notice a slight draught near the outlet at first, but drier air also feels warmer and heats up faster.

Sources

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