London Heat: Why We Need to Think Twice Before Cranking Up the AC

London’s heatwaves are becoming more punishing — and yet, our homes still cling to warmth as if it’s always mid-January. With temperatures rising, it’s tempting to look for a quick fix: air conditioning. But before we all rush to install AC units on every street, it’s worth asking what that really means for our homes — and for our city.

Douglas House: folding sliding timber shutters help reduce solar gain and keep interiors cooler naturally during the summer months.

Why London overheats so easily

A lot of London’s older homes were designed for a different climate and a different way of living. Victorian, Georgian and Edwardian houses were built to hold onto warmth. They relied on fireplaces in every main room, with gaps under doors and windows to feed the flames and help control condensation. Those gaps also brought in fresh air — a built-in source of ventilation that we’ve gradually sealed up with modern windows and doors to keep cold air out in winter.

The result? When heat builds up inside during the summer, it often has nowhere to go. Add to that large single-glazed windows that invite in direct sunlight, poorly insulated roofs that let heat flood in from above, and thick brick walls that absorb the sun’s warmth all day and radiate it back into our rooms all night — like storage heaters you can’t switch off.

But it’s not just the houses. The city itself traps heat. Arup’s Urban Heat Snapshot shows that London’s urban centre is now one of the world’s most extreme urban heat islands — up to 4.5 degrees hotter than surrounding countryside. Neighbourhoods packed with concrete and brick, like Kilburn, can be 7 degrees hotter at night than greener spots like Regent’s Park. It’s a heat that sticks around long after sunset, raising health risks for people in areas with fewer trees and less shade.

What we know already works

In a recent Financial Times piece, the push for more air conditioning across Europe was highlighted — but this comes with consequences. Conventional AC units have outdoor condensers that vent hot air back into the street, making the air outside even warmer. So every new unit can worsen the heat island problem it’s trying to solve.

We don’t need to start with more AC. Other cities have figured out simple, passive ways to keep homes cool long before mechanical cooling existed. Take Barcelona: older flats often have deep balconies that double as built-in canopies, shading windows and doors from the harsh summer sun. External shutters and roller blinds block sunlight before it even hits the glass — but still let breezes flow through.

London can borrow these ideas. A canopy or overhang above a window or door can cut out direct sun. Solar control films or special coatings can reduce heat gain through glass. External blinds or shutters work far better than curtains alone — though good internal blinds paired with modern glazing help too. Integrated blinds sealed within new windows are another clever option, especially for rooflights and glazed doors.

Then there’s airflow. Cross ventilation — opening windows on opposite sides — can pull fresh air through a house. A rooflight at the top of a stairwell can act like a chimney, venting hot air upwards in the evenings and drawing cooler air in.

These fixes aren’t radical. They’re proven, adaptable and often far cheaper to run than blasting AC day and night — saving money and carbon at the same time.

Getting it right with digital design

The best part? We don’t have to guess which ideas will work best. At RISE, we use 3D modelling and digital twins to test them in real homes, virtually first. We can show where a canopy will throw shade at peak sun, how solar film on a south-facing window cuts glare and heat, or how a rooflight can draw warm air up and out.

We can test cross ventilation: where air enters, where it flows, and how it escapes. We can even adjust the size or position of windows to get the airflow just right. And because it’s all done on screen first, there are no expensive regrets later — only smarter, more comfortable homes.

Passive first. Smart tech second.

Sometimes passive measures alone won’t cut it — especially for older people, young children, or anyone living in a building that’s tricky to adapt fully. This is where modern heat pumps come in. Unlike traditional heating systems, an air source heat pump can run in reverse to provide gentle cooling in summer — a far cleaner, more efficient alternative to old-school AC.

It means that once you’ve done the basics — shading, glazing, ventilation — a well-planned heat pump system can take the edge off the hottest days, using far less energy.

And if even that isn’t enough — say you live in a top-floor flat that traps heat or a highly glazed modern building — then a dedicated AC system might still be needed for health and comfort. But it should be the last resort, not the first. Because every new AC unit that blasts hot air into our streets risks making tomorrow’s heatwaves even worse.

So let’s get the order right: passive solutions first, smart tech second, and AC only when we really need it. Less waste, lower bills, cooler homes — and a cooler London, too.

Cooler Homes, Smarter Cities

At RISE, we believe comfort shouldn’t come at the planet’s expense. Every window, canopy or vent is a chance to make a home that stays cool naturally, works better year-round, and helps London breathe a little easier.

Thinking of adapting your home to beat the heat — without ramping up the AC?
We’d love to show you how small design moves can make a big difference.

Let’s start with a conversation — drop us a line or give us a call.

→ architects@risedesignstudio.co.uk
→ 020 3947 5886

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