Scientist's genius hack to cool down a hot car without using air con
UK motorists are being urged to stop reaching for the air conditioning button and check out this super simple hack instead.
An acclaimed scientist has come up with a super smart system for cooling down a cooking car during the increasingly common UK heatwaves. It comes as Brits up and down the nation brace for yet another hot spell this month - with red-hot weather maps showing sizzling temperatures of up to 36C are on the way.
When it's 30°C, within 30 minutes the interior of a vehicle can reach 50°C because of the greenhouse effect. This is where sunlight passes through glass windows heats the interior, but is unable to escape easily, causing inside temperatures to significantly exceed those outside. And it's not just unpleasant: extreme heat can turn everyday items left inside a car into dangerous hazards — they can ignite, leak harmful substances and even explode.
For many, air conditioning is a lifesaver during these sweaty months. However, it can take multiple minutes to cool your car's cabin, and it can be expensive to use for long journeys. In fact, experts over at Kwik Fit report that putting on the AC can increase fuel consumption by 8-10 per cent, or about 0.2 to 0.4 litres per hour.
However, scientist and BBC presenter Hannah Fry took to TikTok to reveal a clever science -based trick that can do the job in seconds - and costs nothing. The mathematician with a PhD in fluid dynamics — the study of how liquids and gases flow — shared her heroic hack on social media just ahead of another UK heatwave.
She explained that instead of immediately turning on the air con, a few simple steps can radically reduce the temperature inside a vehicle almost instantaneously. In her video, Hannah demonstrates the technique by first opening the rear passenger window on the side opposite to the driver, before quickly opening and closing the driver's door several times.
Although this may look a tad odd, the effect is pretty much immediate. Hannah explains: "When you open and close the door, and you do it quickly, the door, as it's moving outwards, sweeps out all of the air that's in the way, creating this area of low pressure."
This process generates what is known as bulk flow, which effectively draws the hot, stale air out of the car. As the rear window on the opposite side is open, fresh, cooler air rushes in to replace the expelled hot air.
Hannah notes that 'it only takes two or three goes and suddenly it's beautifully temperate', making your motor much more manageable in no time at all. This method is particularly useful during heatwaves such as the one currently affecting the UK and parts of Europe, with temperatures reaching record highs.
On July 1, the Met Office confirmed a peak of 34.7 degrees Celsius at St James' Park in London, surpassing previous records for 2025. Hannah Fry 's fluid dynamics hack provides a simple, effective way to beat the heat inside a car without waiting for the air conditioning to catch up.
By understanding how air pressure and flow work inside a vehicle, drivers can cool their cars rapidly and comfortably, even during intense heatwaves. Plus, you'll save on money!
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