With temperatures climbing to 31°C this week, drivers across the country are jumping into scorching cars and immediately making critical mistakes. They’re not just wasting fuel, but potentially putting themselves at risk.
Did you know that leaving your car’s air recirculation button on for more than 30 minutes can cause a CO₂ buildup that could make you drowsy? Or that there’s a specific speed threshold where rolling down your windows actually costs more money than blasting the A/C?
Tom Preston, Managing Director at Hippo Leasing, has shared his top tips on how to keep your car cool in a heatwave, plus the A/C mistakes many drivers make. His tips include:
- The 45mph rule: Below 45mph, open windows are great for fuel efficiency. Above 45mph, the aerodynamic drag costs more than running the A/C.
- Why you should never use the recirculation button in wet weather, but why you must use it in heavy traffic.
- Why turning off Eco and Stop-Start modes is actually necessary during extreme heatwaves to keep the system functioning.
“When people step into their car, many will mistakenly turn the A/C on right away thinking that it will cool them down. However, when you first step into a hot car, try opening your windows for a minute or so before turning on your A/C. This allows trapped hot air to escape, helping your A/C cool the car more efficiently.
Keep windows open for the first minute of driving, too. Whilst you have them open, point the air vents down towards the footwells initially. This is because cool air pushes warm air up and out. Once your car feels cooler, close the windows. Otherwise, you’ll simply pump all the cold air outside.”
Should you use the recirculation button?
“Yes – once the car is feeling cooler and windows are closed, press the recirculation button. It recirculates the cooled air around the car, instead of drawing in hot air from the outside. The result is fast and more efficient cooling.
However, there are a few things to consider:
- Don’t leave it on for too long. If your car is full, CO₂ can build up, which can make the driver drowsy. So, switch it off after around 30 minutes, or crack open a window.
- Avoid using it in wet weather, as it traps humidity and will make your windows fog up fast.
- In heavy traffic, it’s worth switching it on whatever the weather, as it stops fumes from other vehicles getting into your car.”
Are windows or A/C better for cooling the car?
“During a heatwave, A/C is 100% the way to go. While the breeze might feel nice, opening your car windows doesn’t actually cool down the temperature – you’re just moving air around. In contrast, A/C actually removes heat and moisture from the air, resulting in a cooler, more comfortable temperature.
In milder heat, you may get enough relief from the window breeze alone. When driving under 45mph, opening them can be a good option. Drag from open windows is minimal at these speeds, so it won’t cost you much in terms of fuel. Above 45mph, though, open windows create significant drag, so at that point, A/C is actually the more fuel-efficient choice.”
Here are some more cooling tips for drivers:
- “In extreme heat, turn off ‘stop-start’ and ‘eco’ modes if you can. Stop-start can reduce the effectiveness of A/C due to stopping the engine at lights, which also cuts off your A/C. Eco mode can reduce the power of the A/C compressor to save fuel.
- Try not to point the air vents directly at your face. It might feel cool, but it actually leads to poor air distribution around the car. Instead, point them lower so that the cool air can rise naturally.
- Turn on your A/C now and again during winter, too – yes, really! It helps to keep the system healthy by preventing mould and bacterial build-up inside the vents.
- Get your A/C regassed every couple of years. This is when a garage removes the old refrigerant gas from your A/C system and replaces it with fresh refrigerant. Otherwise, you might find that the system loses its cooling power.”
