You switch on the AC, the cabin temperature drops by twenty degrees, and the fuel gauge needle moves faster than you expected. How much fuel does air conditioning really use, and how much of it is just a myth repeated on forums without a single hard number? ADAC has measured data that give a clear answer, and we will translate those figures into a concrete amount in convertible marks at current BiH fuel prices.
This guide was prepared by Auto Gas Gaga workshop in Banja Luka, based on technical data and years of experience servicing AC systems on all vehicle types.
Table of Contents
- How Much Fuel Does AC Really Add to Consumption
- City, Motorway and Traffic Jams - Where AC Uses the Most Fuel
- AC or Open Windows - What Is Actually Cheaper
- Automatic vs Manual AC - the Difference in Consumption
- Eight Tips to Reduce Fuel Consumption in Summer
- How Much Does AC Cost You in KM per Year
- When AC Uses More Fuel Than It Should - Signs of a Fault
- Frequently Asked Questions
- Related Articles
How Much Fuel Does AC Really Add to Consumption
A car's air conditioning uses fuel because the AC compressor draws power directly from the engine. The compressor is driven by a belt attached to the crankshaft, and it needs between 2 and 6 horsepower to operate, depending on the system size and the cooling demand. On a small city car with a 75 hp engine, the 4-5 hp the compressor takes represents roughly 6% of total engine output. On a larger car with 150 hp, the same compressor takes a smaller percentage and the impact on consumption is proportionally lower.
ADAC tests show that air conditioning increases fuel consumption by 10-15%, depending on the model and driving conditions. In absolute terms, that means 0.3 to 2.4 litres per 100 km of extra consumption. The range is huge because it depends on where and how you drive, what engine you have, and how efficient the AC system itself is.
On short urban trips the effect is most pronounced. The engine runs at low revs, the AC compressor constantly draws power, and you sit at a traffic light with the engine burning fuel solely to run the air conditioning. On longer motorway stretches, the AC cools the cabin to the set temperature once and then operates at reduced load, so its impact drops to a minimum.
A factor many people forget is the initial cool-down. When you get into a car that has been sitting in the sun with the interior heated to 60-70 degrees, the AC has to work intensively for the first 10-15 minutes to bring the temperature down. That period consumes the most fuel. If your average trip lasts 15 minutes, the AC runs at full capacity for most of that time and consumption is at its peak. That is why it is important to understand that the figure "10-15% more" does not tell the whole story. The real impact depends on trip length, the starting cabin temperature, and the speed you are travelling at.
City, Motorway and Traffic Jams - Where AC Uses the Most Fuel
A specific test on vehicles with 90-100 hp engines, which corresponds to the average BiH car, produced precise figures worth knowing.
How Much Fuel Does AC Use on the Motorway
On the motorway at 130 km/h, AC increases consumption by just 0.2-0.3 litres per 100 km. At that speed the engine already runs in a higher regime and the AC compressor is a negligible extra load. Air flowing through the condenser at the front grille cools the system efficiently, so the compressor does not need to run at full power. This is why AC barely affects the fuel budget on a longer journey.
In city driving at an average speed of 19 km/h, typical of a morning rush hour in Banja Luka or Sarajevo, manual AC uses as much as 2.4 litres per 100 km more. That is a huge difference. At 50 km/h in normal urban traffic, the extra consumption from AC drops to around 1-1.5 litres per 100 km.
The key is that AC uses roughly the same amount of energy regardless of driving speed, but at lower speeds the engine is less efficient, so the relative impact of the AC rises. On the motorway the engine produces more horsepower and the AC compressor is a small fraction of that total output. In traffic jams the engine barely turns over and the AC compressor becomes a significant consumer. Additionally, in city driving the car stops and starts more often, and every pull-away from standstill requires more fuel when the AC compressor is simultaneously loading the engine.
AC or Open Windows - What Is Actually Cheaper
This is an age-old debate and the answer depends on the speed you are travelling at.
Does AC Use More Fuel Than Open Windows
Up to 60-70 km/h, open windows are the cheaper option. Aerodynamic drag at those speeds is low, and natural airflow provides enough cooling at zero fuel cost. AC at the same speed increases consumption by about 1-1.5 litres per 100 km.
Above 80 km/h the situation reverses. Open windows at that speed create significant aerodynamic drag that can increase fuel consumption by 5-8%, which is comparable to running the AC. On the motorway, at 120-130 km/h, open windows use more fuel than AC because aerodynamic drag is proportional to the square of speed. Double the speed means four times the air resistance.
The practical rule is simple: in the city and on slow roads open the windows; on the open road and motorway switch the AC on. Your wallet will thank you either way. A driver's-side window cracked open two fingers' width gives enough circulation in the city without major drag, while fully open windows on all sides create noise and cabin turbulence that makes conversation and concentration difficult.
Automatic vs Manual AC - the Difference in Consumption
Automatic AC is about 40% more efficient than manual AC in city driving. The reason is that automatic AC self-regulates compressor output according to the current cabin and outside temperature.
Manual AC knows only two states: on or off. When it is on, the compressor runs at full power regardless of whether the cabin has already cooled to the desired temperature. A driver with manual AC usually adjusts the blower speed, but the compressor works the same either way. Automatic AC, on the other hand, uses temperature sensors and an electronically controlled compressor clutch to fine-tune the cooling. Once the cabin cools down, the compressor runs at reduced power or switches off temporarily.
In city traffic jams, where the AC has to run for a long time, the difference is measurable: automatic AC adds 1.2-1.3 litres per 100 km, while manual AC adds 2.4 litres. On the motorway, the difference between automatic and manual AC is negligible because both operate at lower loads.
If your car has manual AC, there is a simple trick: once the cabin cools down, switch the AC off for a couple of minutes, then turn it back on. You are simulating what automatic AC does by itself. It is not perfect, but it will help you save 0.5-1 litre per 100 km in city driving compared with leaving manual AC on constantly.
Eight Tips to Reduce Fuel Consumption in Summer
Here are concrete steps that reduce the impact of AC on consumption without sacrificing comfort. Each one can be applied immediately, with no investment needed.
How Parking in the Shade Reduces Fuel Consumption
1. Park in the shade whenever possible. A car that has been standing in the shade has an interior temperature 15-25 degrees lower than one in direct sunlight. The AC cools it in 5 minutes instead of 15, and the first 10 minutes are precisely the period when AC consumes the most fuel. If there is no shade, use a reflective windscreen sunshade. These reflective screens can reduce dashboard temperature by 20-30 degrees and protect the plastic from becoming brittle due to UV radiation.
2. Ventilate the car before switching on the AC. When you get into a hot car, open all windows for 30-60 seconds and let the hottest air escape. Air at 65 degrees is lighter than air at 30 degrees and leaves the cabin on its own. Only then close the windows and switch the AC on. This step shortens the maximum-cooling phase and reduces overall fuel consumption because the AC starts from a lower initial temperature.
3. Set the AC to 22-24 degrees, not minimum. Every degree below 22 means the compressor has to work harder. The difference between setting the AC to 18 and 23 degrees can amount to 0.5-1 litre per 100 km of extra consumption. The body adapts quickly to 23 degrees, and that temperature is comfortable enough for driving without sweating.
4. Use air recirculation in the city. When you activate recirculation, the AC cools already-cooled cabin air instead of hot outside air. This is significantly more efficient because the AC does not have to bring the temperature down from 38 degrees of outside air, but from 25 degrees already in the cabin. On the motorway, switch to fresh air every 15-20 minutes to refresh the oxygen inside, then go back to recirculation.
5. Switch the AC off 3-5 minutes before the end of your trip. The system retains its coolness without the compressor for several minutes. This trick also helps the evaporator dry out, which prevents the growth of bacteria and mould that cause unpleasant odours. Leave the blower running, just press the AC button off.
6. Maintain correct tyre pressure. Properly inflated tyres improve fuel economy by an average of 0.6%, and in some cases up to 3%. In summer, when the tarmac is hot, underinflated tyres create greater rolling resistance. Check pressure once every two weeks, always on cold tyres in the morning. You can read more about tyre pressure and maintenance in our guide to tyres and pressure.
7. Avoid aggressive driving in summer. Aggressive driving reduces fuel economy by 15-30% on the motorway and 10-40% in stop-and-go city traffic. Combined with AC, that is a double hit on the fuel budget. Smooth driving with traffic anticipation is a free saving measured in hundreds of KM per year. More specific techniques for economical driving can be found in our guide to reducing fuel consumption.
8. Check that the right engine oil is in your engine. The wrong oil viscosity reduces engine efficiency by 1-2%. Combined with AC use in summer, that is an extra cost that adds up over a year. Use the oil specified by the manufacturer for your engine and the season. If you are not sure which is the right one, see our guide to choosing engine oil.
How Much Does AC Cost You in KM per Year
Let us translate percentages into hard cash. According to data from cijenegoriva.ba as of 13.06.2026, the average diesel price in BiH is 3.03 KM per litre, petrol B95 is 2.92 KM per litre, and LPG is 1.41 KM per litre.
How Much Does AC Cost in KM per 100 km
Take an average BiH driver with a combined driving pattern: 60% city, 40% open road. Their baseline consumption is 7 litres of diesel per 100 km. With AC during the summer months, consumption rises to an average of 7.8-8 litres per 100 km, roughly 0.8-1 litre more.
Per 100 km, that is 0.8 to 1 litre of diesel, i.e. 2.40-3.03 KM of extra cost. For a petrol driver with the same baseline, the AC cost per 100 km is 2.34-2.92 KM. For LPG drivers, the same extra litre of gas costs 1.41 KM, which is almost half the diesel or petrol figure.
The average BiH driver covers around 15,000 km per year. If they use AC for 4-5 months (May to September), that is roughly 5,000-6,000 km with the AC on. On diesel, the annual AC cost is 120-180 KM. On petrol, 117-175 KM. On LPG, 70-85 KM. That is the price of comfort, and for most drivers it is entirely justified. The question is simply whether that cost could be 20-30% lower with smarter AC use, and the answer is yes, if you apply the tips from the previous section.
LPG drivers have a clear advantage here: LPG is significantly cheaper than diesel and petrol per litre, so the cost of running the AC is proportionally lower. If you are interested in how much an LPG conversion would save in your specific case, see our LPG savings calculator.
When AC Uses More Fuel Than It Should - Signs of a Fault
An AC system that is not working properly uses more fuel because the compressor runs longer and under greater load trying to reach a temperature the system cannot achieve. Here are the signs that your AC is wasting fuel.
The AC blows lukewarm air. If the air from the vents is not cold even after 5 minutes of operation, the refrigerant level is probably low. The compressor cycles on and off in short bursts, consuming fuel but not achieving cooling. A refrigerant top-up solves the problem in most cases. If refrigerant is being consumed too quickly, there is a leak somewhere that needs to be located and repaired.
Unpleasant smell when the AC starts. Mould on the evaporator does not directly affect consumption, but a dirty cabin filter, which often accompanies this problem, restricts airflow, forces the compressor to run longer, and increases consumption. Replacing the cabin filter is the cheapest service job that improves both AC efficiency and cabin air quality. Read more about cabin filters in our cabin pollen filter guide.
The compressor sounds louder than usual. Compressor bearings that are nearing the end of their life create extra resistance, the compressor draws more engine power, and that means more fuel. An unusual noise from the front of the engine when the AC is on requires a workshop inspection.
Fuel consumption has jumped sharply in summer with no change in driving habits. If you are using 1-2 litres per 100 km more than last summer while driving the same way, the AC is the prime suspect. Refrigerant leaks, a clogged condenser, or a worn compressor are the most common causes. A condenser clogged with dust, insects, and road grime loses its ability to dissipate heat, so the compressor has to work harder. Cleaning the condenser with compressed air is a simple job that can noticeably improve cooling efficiency. A detailed guide on what an AC service covers and when to have it done can be found in our AC service and refrigerant recharge guide.
A faulty AC system does not just consume more fuel; in the long run it can damage the compressor or condenser, and those repairs are significantly more expensive than regular servicing. Summer is the right time for an AC check. Book an appointment and make sure your air conditioning is working as it should.
Frequently Asked Questions
How much fuel does AC use per 100 km?
AC uses 0.2-2.4 litres per 100 km more, depending on driving conditions. On the motorway it is just 0.2-0.3 litres, in city traffic up to 2.4 litres. On average, for combined driving, count on 0.8-1 litre per 100 km of extra consumption.
Is it better to open the windows or switch the AC on?
Up to 60-70 km/h, open windows are more economical. Above 80 km/h, AC uses less fuel than open windows due to aerodynamic drag. On the motorway always use AC instead of windows.
What temperature should the AC be set to for the lowest consumption?
The optimal temperature is 22-24 degrees. Every degree below 22 means extra compressor work and higher fuel consumption. The difference between setting the AC to 18 and 23 degrees can amount to 0.5-1 litre per 100 km.
Does automatic AC use less fuel than manual?
Yes, automatic AC is about 40% more efficient than manual in city driving. Automatic fine-tunes compressor output according to temperature, while manual runs at full power when switched on. On the motorway the difference is negligible.
Why does AC use more fuel in summer than in winter?
In summer the gap between the desired cabin temperature (22-24 degrees) and the outside temperature (35-40 degrees) is much larger than in winter, when the AC mainly serves to demist the windows. A larger temperature difference requires more intensive compressor work and more fuel.
Does AC use fuel when the car is idling?
Yes. When the engine is idling, the AC compressor uses approximately 0.5-0.8 litres per hour. In city traffic with frequent stops this adds up. At a 2-minute red light with the AC on, you use about 20-30 ml of fuel on the AC alone.