A £100,000 Retrofit Couldn't Keep This London Home Cool in the Heatwave

Catherine Katzka retrofitted her 1960s family townhouse in Sydenham, south-east London in 2022, spending approximately £100,000 on triple glazing, photovoltaic (PV) panels, an air source heat pump, and external blinds. The project cut her energy bills by 70% and eliminated her gas supply entirely.

But during June's heatwave, the inside of her home hit 28C after three days of 35C sunshine.

The culprit was her mechanical ventilation heat recovery (MVHR) system, which is designed to circulate fresh air and recover heat in winter. On hot days, it simply circulates London's warm outdoor air through the house instead.

"I'm starting to regret not adding air con," Katzka said.

Her experience reflects a wider problem. London's housing stock was built for cold winters, not hot summers, and the urban heat island effect makes the capital's built-up areas run even hotter than surrounding areas.

The Greater London Authority estimates more than one million existing properties in London need retrofitting for heat. But a "huge funding gap" remains, according to GLA climate adaptation manager Dan Bicknell.

Katzka said finding skilled labour willing to carry out the work was one of the biggest challenges, and coordinating the project herself was "almost a second job."

The city's retrofit supply chain "lacks coordination and a whole house perspective," a Department for Energy Security and Net Zero report warned last year.

The GLA is due to publish its Heat Risk Delay Plan this summer, setting out a city-wide framework for managing overheating. In the meantime, Katzka says adding air conditioning powered by her PV panels is probably her next step.