On sweltering days, getting into a car that has been baking in the sun can be an unbearable experience. Mathematician and broadcaster Hannah Fry has shared a simple hack that has been viewed over 10 million times: open a rear diagonal window, then rapidly waft the car door back and forth without fully closing it. The motion creates low pressure that draws out hot air and pulls in cooler air from outside.
A journalist tested the trick on a 34°C May day in London. After three rounds of vigorous door-waving, the car's interior felt marginally improved, but the effect was limited because the outside air was also very hot. Moreover, the physical effort raised the journalist's body temperature, partially offsetting the cooling benefit.
Dr Tom Crawford, a mathematician at Oxford and Cambridge, explained that the method's effectiveness depends on three factors: wafting the door quickly enough to create low pressure, opening the rear window sufficiently to allow airflow, and a significant temperature difference between inside and outside air. If the outside air is as hot as the inside, the swap won't help.
For best results, the trick should be used early in the day when outside air is cooler. The RAC also recommends pointing air vents downward to let hot air rise, using the 'external' setting on air conditioning to bring in fresher air, and opening windows. Once the car is cooler, switch to recirculated air to maintain comfort.
