Why Car Interiors Get So Hot in the Summer

During the summer months, climbing into a hot car can feel almost unbearable. Even if you’ve been parked in the shade, you’re still likely to feel the heat when you’re ready to drive – but why exactly does getting into your vehicle feel like stepping into a walk-in oven during the summer?


The answer is quite simple, and we’ve got science to thank for understanding this: the greenhouse effect. That’s right – the same effect that keeps heat within our atmosphere (thereby keeping our planet at a rather cosy temperature) is also responsible for drastically increasing the interior temperature of your car during summer.

The windshield suntrap

The windshield of your vehicle doesn’t simply allow you to have a wide and unobstructed view of the road. It also allows natural sunlight to enter unobstructed into the interior of your car. Shortwave radiation from the sun can pass through clear surfaces like windows without warming them up too much – therefore, your windshield won’t feel particularly hot to the touch.

However, darker colored objects which sunlight encounters (such as the steering wheel, dashboard and seats) are heated much more intensely on account of having a lower albedo. These heated objects will then heat the air around them in the interior via conduction and convection.

How hot does it get in an enclosed car?

According to a 2002 study by professors at San Jose University, the average temperature in an enclosed car with a basic interior will rise by approximately 19°F after just 10 minutes of exposure to the sun. After a further 10 minutes, the temperature can be expected to increase a further 29°F. It’s worth noting that two-thirds of temperature spikes occur within the first 20 minutes of a vehicle being left in direct sunlight, with temperature increases tapering down slightly after this initial period.

This highlights a rather sobering reality: children, the elderly or pets should never be left in a parked car without sufficient air conditioning, even if it only seems like leaving them there for a minute or two – because this precisely when the bulk of those temperature rises happen. Hot cars are a hazard and can result in issues like heat stroke, hyperthermia and even death – particularly in vulnerable persons like the elderly or young infants. Children, in particular, are more susceptible as their body temperatures rise 3-5x faster than the average adult.

Can I just open some windows?

Unfortunately, opening windows does little to reduce the temperature in the interior of a car. The same 2002 study from San Jose University found that the temperature of a car with its windows closed will rise at a rate of 3.4°F every five minutes. With the windows down, this drops by just 0.3°F to 3.1°F – a negligible amount, we’re sure you’ll agree.

Keeping cool

There are lots of ways to the interior of your vehicle cool – air conditioning and sunshades are just two examples. If you’d like to know more about how you can make your vehicle more comfortable during those hot summer months, why not get in touch with our team today? Our friendly, experienced professionals will be more than happy to help.