Sylvie Willis
It is a well-known fact that air conditioning uses extra fuel when driving. The air conditioning system works similarly to a refrigerator, where a high-pressure element forces the gaseous refrigerant (coolant) into the condenser with the compressor, which is driven by a belt connected to the engine. This process heats the compressed refrigerant, which is then cooled by the condenser and turned into a liquid under pressure. The pressurised refrigerant, now a liquid, is forced through the expansion valve and evaporator, turning into icy cold gas. The amount of fuel used by the air conditioning depends on various factors, such as the make and model of the car, the outside temperature, the speed of the blow, the cabin size, and driving conditions. Research suggests that driving with open windows is more economical than using air conditioning when travelling at speeds of 45-55 mph or less. However, at higher speeds, using air conditioning is more fuel-efficient than open windows due to the extra drag created. Overall, the increased fuel consumption due to air conditioning can be up to 10%, and regular maintenance of the air conditioning system can help improve its efficiency.
| Characteristics | Values |
|---|---|
| Increase in fuel consumption | 8-10% or 0.2-0.4 litres per hour |
| Fuel efficiency at higher speeds | Air con is more fuel-efficient than open windows |
| Air con blow speed | Higher speed places greater strain on the engine, using more fuel |
| Cabin size | Larger cabins take longer to cool, requiring more effort from the air con system |
| Driving conditions | Air con is less efficient in stop-start traffic than at steady speeds |
| Travelling speed | At speeds over 45-55 mph, air con is more economical than open windows |
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What You'll Learn
Air con vs. open windows
When deciding whether to use air conditioning or open your windows, there are several factors to consider. Firstly, air conditioning can increase fuel consumption by around 8-10%, or 0.2-0.4 litres per hour, as the system is powered by the engine, which uses fuel to run. This increase in fuel consumption may be more noticeable on short journeys, as the air conditioning has to work hard to bring the internal temperature down.
However, driving with the windows down can also impact fuel efficiency, especially at higher speeds. Research suggests that driving with the windows open is more economical at speeds of 45-55 mph or less, as running the air conditioning at low engine speeds creates extra demand on the engine. Above these speeds, it is more fuel-efficient to use air conditioning as the drag caused by open windows increases resistance.
To reduce fuel consumption, it is recommended to park in shady areas, drive with the windows down initially to remove hot air from the cabin, and then close the windows and turn on the air conditioning. Additionally, maintaining proper tyre pressure and avoiding heavy loads in the vehicle can also improve fuel efficiency.
It is worth noting that the impact of air conditioning on fuel economy may be minimal if used sparingly, and other factors such as driving style can have a more significant impact.
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Air con and fuel economy
Air conditioning can increase fuel consumption by between 8% and 10%. This amounts to between 0.2 and 0.4 litres of fuel per hour.
However, there are many factors that influence the amount of fuel used by air conditioning systems. For example, the size of the cabin will affect how long it takes to cool down, with larger cabins requiring more effort from the air conditioning system. Similarly, driving conditions will impact fuel consumption—air conditioning is likely to be less efficient in slow-moving traffic than when driving at a steady speed.
The speed at which you are travelling will also determine whether it is more fuel-efficient to use air conditioning or to open a window. Running the air conditioning at low engine speeds creates extra demand, so it is more economical to open the windows when driving at 45-55 mph or less. However, at speeds over 45-55 mph, the drag caused by open windows increases resistance, making it more fuel-efficient to use the air conditioning.
To reduce the amount of power used by your air conditioning, it is recommended to park in a shady area, drive with the windows down for a few minutes before using air conditioning, and only use accessories for the minimum amount of time.
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Air con and engine load
Air conditioning can increase fuel consumption by placing an extra load on the engine. The air con system is powered by the engine, which uses fuel to run. When the air conditioning is switched on, its components put an extra load on the engine, causing it to work harder and use more fuel. This is particularly noticeable when the engine is running at low speeds, such as in slow-moving traffic or when stopping and starting.
The compressor, which circulates refrigerant to cool the air, is a significant contributor to the increased fuel consumption. Running the air con at full blast or having certain vent settings that make the system work harder will also increase fuel consumption. The size of the cabin also plays a role, with larger cabins taking longer to cool down and requiring more effort from the air conditioning system.
To reduce the load on the engine and minimise extra fuel consumption, it is recommended to reduce reliance on air conditioning. This can be done by parking in shady areas, opening windows when travelling at low speeds, and adjusting the temperature or flow rate of the air conditioning once the cabin has cooled down.
The impact of air conditioning on fuel economy has been a topic of debate, with some studies estimating an increase in fuel consumption of between 8% and 10%, while others suggest it could be as low as 5%. However, the extra load on the engine caused by air conditioning is undeniable, and drivers can take steps to mitigate its impact on fuel usage.
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Air con and fuel costs
Air conditioning can increase fuel consumption by between 8% and 10%. This amounts to an estimated increase of 0.2 to 0.4 litres of fuel per hour.
There are several factors that influence the amount of fuel used by air conditioning. Firstly, the speed at which you are travelling matters. When driving at speeds of 45-55 mph or less, it is more fuel-efficient to open the windows. This is because running the air conditioning at low engine speeds creates extra demand, resulting in increased fuel consumption. However, at speeds above 45-55 mph, it is more economical to use the air conditioning as the drag from open windows causes increased resistance at high speeds.
The air con blow speed also affects fuel consumption. Running the air conditioning at full blast or using certain vent settings that make the system work harder will place a greater strain on the engine, resulting in higher fuel usage. Additionally, the cabin size matters. Larger cabins will take longer to cool down, requiring more effort from the air conditioning system and, consequently, more fuel.
To reduce fuel consumption, it is recommended to park in shady areas, drive with the windows down for a few minutes before using air conditioning, and reduce reliance on air conditioning by adjusting the temperature or airflow once the car has cooled down.
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Air con and fuel-saving tips
Using air conditioning can increase fuel consumption by between 8% and 10%. This is because the air conditioning system is powered by the engine, which uses fuel to run. When the air con is on, the engine has to work harder, using more fuel.
Air Con vs Open Windows
Whether it's more fuel-efficient to drive with the windows open or the air con on depends on your speed. At speeds over 45-55mph, it's better to use the air con as the drag caused by open windows increases resistance. At lower speeds, it's more economical to open the windows as running the air con creates extra demand on the engine.
Other Tips to Reduce Fuel Consumption
- Park in a shady area to avoid the sun heating up your car.
- Drive with the windows down for a few minutes to clear hot air from the cabin, then close them and turn on the air con.
- Keep your tyres properly inflated. Underinflated tyres increase drag, while overinflated tyres can lead to blowouts.
- Remove heavy loads from your car as these create a drag effect, using more energy to keep the car moving.
- Drive efficiently. The way you drive can have a big impact on fuel efficiency.
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Frequently asked questions
Yes, air conditioning uses extra fuel. The amount of extra fuel depends on a variety of factors, including the make and model of your car, the outside temperature, the temperature setting, the speed at which you are travelling, and the size of the cabin.
Estimates suggest that using air conditioning can increase fuel consumption by 5-10%. However, this varies depending on the factors mentioned above. For example, driving with the windows down at high speeds can increase fuel consumption by 20%, while the impact of air conditioning on hybrid cars is almost twice as much, with fuel efficiency dropping 6.1% in a hybrid car on average.
To reduce the amount of extra fuel used by air conditioning, you can:
- Maintain your air conditioning system by keeping up to date with services and regassing when necessary
- Avoid using air conditioning at low engine speeds (below 45-55mph) as this creates an extra demand on the engine
- Avoid driving with the windows down at high speeds as this creates drag, causing the engine to work harder
- Improve your driving style by gently accelerating and using the highest safe gear, ensuring your tyres are inflated to the correct pressure, and removing any heavy loads from your vehicle
