Does Your Car's Air-Con Use Fuel?

With the UK’s hottest ever temperature having been smashed last week, it’s only understandable that those commuting to and from work or undertaking long journeys in their car would wish to cool down and gain some respite from the baking sun. Cue the age-old debate: what’s better for your fuel efficiency, turning on the air-con or simply winding down the windows?

That all depends, apparently. When driving at slower speeds and through built-up areas or on winding country roads, opening your windows could be more beneficial for your fuel efficiency than air-con. However, as soon as you hit the motorway and open up the engine, rolling the windows up and switching on the AC is advisable for those looking to travel in comfort without wasting fuel.

The case for and against AC

It’s fairly common knowledge that running the AC can compromise fuel efficiency – but so too can opening up the windows while in motion, since the lag caused by the wind resistance means your engine has to work harder. So what’s the tipping point between the two? In which situations should you roll down the windows, and in which should you flick on the air-con?

According to The Air Conditioning Company, the magic number for fuel efficiency is 55mph. Anything lower than this will benefit from simply letting in some fresh air by opening the windows, but anything above it will suffer from too much lag. In those cases, the 8%-10% of fuel efficiency lost to air-con will still be preferable to greater percentages of energy lost to opening the windows.

Other tips for boosting fuel efficiency

As well as remembering that 55mph is the tipping point for AC use, drivers can employ a number of other handy habits to ensure their car is running as smoothly and efficiently as possible. These include:

• Using the AC to maintain a cool temperature rather than achieve one (since it will have to work harder and conserve more fuel to do so)
• Opening the windows for a few minutes when first entering a car on a hot summer’s day to clear it of the majority of the overheated air (see the point above)
• Testing the AC for five or ten minutes every two weeks to ensure it is working sufficiently well to affect the interior temperature of the car
• Remembering the importance of lubricants when it comes to keeping the engine and air-con running smoothly and without any problems
• Minimising the use of accessories (such as the radio, windscreen demister or cigarette lighter) to conserve fuel as much as possible

Of course, the most effective way of improving fuel efficiency and reducing your environmental impact is, unsurprisingly, through a car which consumes less fuel. Among petrol and diesel options, it’s certainly true that some makes, models and sizes are better than others, with smaller categories being clearly ahead of their larger and more cumbersome counterparts. However, hybrids and electric vehicles (EVs) remain the ideal option for reducing fuel consumption and transitioning to a cleaner tomorrow.