This has led us to do some digging, just how much fuel are we using and how much does it affect our miles per gallon (mpg) score? And is it actually more cost effective to just simply open the window? The big questions answered at the All Car Leasing blog!
How much fuel air conditioning uses has many factors - too many factors really, the able to confidently give a score for any car. Let's break it down
It's the vehicle's engine that drives the pump that produces the conditioned air, the engine needs to do this at the same time as provide power to wheels and to the electronics and so on, if the engine is large and powerful it can do it with ease and not use much more fuel to complete the task but a smaller engine such as a 1.0i does't have power to spare so it will drink more fuel to get the job done.
How much air you want to be pumped out and what temperature that air is set is all play a part in how hard your air conditioning system is working the engine. If you've got climate control this can be even greater.
An air conditioning system that has been serviced recently and in good nick will work better and more efficiently than one that hasn't.
A warmed up engine which has reached optimum temperature performs better. A cold engine or an engine that is overheating does not.
Based on all of the above factors, generally using air conditioning could reduce 5%-10% of the your mpg or 1-3mpg in simpler terms. Using air conditioning doesn't really use that much fuel but if you used it all the time that cost would add up significantly. If you only really use it when it's too hot or too cold then the extra cost is pretty much minimal.
This question is an age old debate - will it cost less fuel keeping windows open or having the air con on? Believe it or not, General Motors and SAE worked together to find the answer as did popu;lar TV series Mythbysters with the answer being... windows down!
Indeed, in a test using a wind tunnel it was concluded that having windows down used less fuel than having air conditioning on, regardless of speed. So, if you're looking to save some pennies then go for it, however to drive in comfort we would of course recommend using air con as having windows down is noisy, potentially dangerous and uncomfortable at high speeds, here's a graph showing the results.
So there we have it. Which one do you prefer on a hot day - air con or windows down?