As we all know, the (glorious?) British Summer takes up three months of the year, so you're bound to need your car's air-conditioning system (or 'air con', for short) at some point on one of those hot days.
But with fuel prices soaring, the question is: does putting the windows down actually save more fuel than using the air conditioning?
Well, research says that it depends on how fast you're going.
Air Conditioning vs Open Windows
45mph is the magic number here.
If you're travelling at speeds of 45mph or less, it's more economical to open your windows. That's because running the air conditioning at this low engine speed creates an extra demand, so opening the windows is the best option.
If you're travelling at speeds of over 45mph, it's more economical to make use of the air conditioning system. That's because the extra drag caused by opening your windows will mean your car faces increased resistance at high speeds.
Of course, every car is going to be a little different and at the end of the day, the 45mph figure is only a rough guide, but it's still a fairly good marker to follow.
Why Does Air Conditioning Use Fuel?
Without going too much into the science behind it, air-conditioning leads to increased fuel consumption because in order for the system to work, some energy is required to carry the cool gas into the cabin of your car.
It might not seem like it would make much of a difference, but believe it or not, using air con can increase your fuel consumption by as much as 10%, and opening the windows when at higher speeds can increase it by as much as 20%.
Meanwhile, a study by Emissions Analytics found that the impact of air-conditioning on hybrid cars was almost twice as much, with fuel efficiency dropping 6.1% in a hybrid car on average, compared to just 3.8% for a standard petrol car and 4.6% for a diesel. Just something to bear in mind if you happen to drive one . . .
What About Air Pollution?
Okay, so let's suppose you're in a slow-moving line of traffic in hot weather . . .
In these situations, it's best advised that you avoid using air con or opening your windows altogether so that you don't end up breathing in the polluted air.
Yet we know that might not be the most comfortable thing to do temperature-wise, so what you could do instead is turn on the air con but close the air vents so that the air con only recycles the cabin air rather than drawing in the harmful air from outside.
Final note: don't forget to have your vehicle's air conditioning system serviced regularly. This should be done every two years to ensure that the system is running efficiently.
FAQs
How much more gas does AC use?
AC can use up to 10% more gas.
Does turning off aircon save fuel?
Absolutely, so only use it when needed.
Does air conditioning improve MPG?
No. Air conditioning can increase fuel consumption by as much as 10%.