A woman in a hot car.
It’s remarkable how, when it gets a little warm outside in the summer, the interior of your car can become a blazing inferno. A big reason for the discrepancy between the outside air temperature and the interior of your car is the same reason the planet is getting warmer: the greenhouse effect.
When you close your car windows and it's warm outside, the heat can’t escape because longwave radiation can’t pass through windows as easily as shortwave radiation. That’s why temperatures can go from comfortably cool when you get out of your car to blazing within minutes.
In fact, if it’s 80 degrees outside, it only takes 10 minutes for the car’s inside temperature to rise to 99 degrees and an additional hour to reach 137 degrees. That’s why it’s important never to leave your pet in the inside of your car, even when it feels cool outside.
A man in a hot car.via Canva/Photos
How to cool a hot car in the summer
So, how do you cool your car down when it feels like a volcano inside in the middle of summer? Victoria Fenn Alvarado, a reporter with Canada’s The Weather Network, shared a science-based hack to cool your car even faster than blasting the air conditioner. First, you open the passenger-side window down. Then you open the driver's side door and step outside of the car. "Open and close the door paridly, about seven to 10 times. Once you complete his step, you can step inside your vehicle, and now you can drive away comfortably," Alvardo said.
It may look unusual to others in the parking lot to see you using your car door like a massive fan, but the hack is effective because it utilizes forced convection to replace the hot air with cool, fresh air. “Opening and closing the door acts as a pump, allowing warm air to exit rapidly. Paired with having the window open on the other side, this motion creates a pressure drop inside the vehicle, pulling in outside air, essentially replacing the warm air with fresh air,” Alvarado continues.
Hannah Fry further explained the phenomenon in a viral TikTok video. Fry is Professor of the Public Understanding of Mathematics at the University of Cambridge and the host of numerous popular podcasts and television shows.
How to cool your hot car using forced convection
@fryrsquared That age-old dilemma of choosing between having a non-sweltering car or baffling a passerby because you look like a fool who doesn't know how to use a door
“The reason why it works is that when you open and close the door, especially if you do it quickly, the door, as it's moving outwards, it sweeps out all of the air that's in its way, creating this sort of area of low pressure that you get here,” Fry said. “And then that sets up something called bulk flow, which is where all of the hot, sweaty, horrible air inside the car is drawn outwards.”
The hack is one of the strange things that seems obvious, but most people probably haven’t considered. However, once you see it in action, it’s impossible not to think: Why didn’t I think of that? Here’s to enjoying the rest of your summers, knowing that even if it gets a bit warm outside, you always have a cool car to look forward to.