Is it better to drive with windows down or AC on?

It depends on speed and conditions: at low city speeds, driving with the windows down is usually more efficient; at highway speeds, using the air conditioner (AC) typically uses less energy than the added aerodynamic drag of open windows. Factors like outside temperature, humidity, vehicle type, and whether you drive a gas car or an EV also matter. Below, we explain how to choose the most efficient and comfortable option for your trip.

What really determines the better choice

The decision comes down to a trade-off between aerodynamic drag and climate-control load. Opening windows disturbs airflow around the vehicle, increasing drag that rises steeply with speed. Running AC adds a mechanical or electrical load—on an engine in a gasoline car, or on the high-voltage battery in an EV—that can reduce fuel economy or range. The balance point shifts with speed, weather, and vehicle design.

Key variables at a glance

These are the primary factors that influence whether windows down or AC on is better in your specific situation.

• Speed: Below roughly 35–40 mph, the drag penalty from open windows is small; above about 45–50 mph, drag rises quickly and AC often wins.
• Vehicle shape: Boxier SUVs and trucks suffer more from open-window drag than sleek sedans or coupes.
• How much the windows are open: A small crack for ventilation costs far less than fully lowered panes.
• AC setting and mode: Lower fan speeds, moderate temperatures, and “recirculate” mode reduce compressor work.
• Heat, sun, and humidity: High solar load and humidity increase AC demand; dry, mild days favor windows.
• Air quality and allergies: AC with cabin filtration can be preferable in polluted or high-pollen environments.
• Powertrain: In EVs, strong AC use directly trims range; in hybrids, the impact varies with battery state and system design.
• Trip length: Short, hot starts are AC-intensive; pre-cooling can shift the balance toward AC efficiency.

Understanding these variables helps you tailor your choice to the moment. In real-world driving, the “best” option can change even within a single trip as speeds and conditions shift.

What the research and guidance say

Government efficiency guidance and independent tests point to a consistent rule of thumb: open windows are generally fine at low speeds, while AC is often the better bet at highway speeds. The U.S. Department of Energy notes that AC use can reduce fuel economy significantly in hot weather—often in the 5–20% range, and more in extreme heat—while open windows increasingly hurt efficiency as speeds rise. Controlled tests (including industry and media experiments over the past two decades) have found that at around 55–70 mph, the drag from fully open windows can equal or exceed the energy penalty of using AC, though results vary by vehicle and setting.

For EVs, cabin cooling can trim range by roughly 5–20% in hot conditions; at very high temperatures and strong cooling settings, the impact can be higher, especially on short trips that start with a hot-soaked cabin. Modern vehicles mitigate some of this with efficient, variable-speed compressors, heat pumps, and smarter climate controls, which can narrow the gap between the two choices.

Recommendations by scenario

City and low-speed driving (generally under 35–40 mph)

Windows down is typically more efficient and perfectly reasonable for comfort on mild days. If it’s hot, try using the fan with “recirculate” and a moderate AC setting; you may still beat the penalty of fully open windows at these speeds.

Suburban and mixed driving (35–50 mph)

This is a gray zone. Partially opening windows or using AC on a light, recirculated setting often nets similar efficiency. If you’re edging toward the higher end of this range, lean toward AC—especially in taller or boxier vehicles.

Highway driving (about 55 mph and above)

Use AC and keep windows up for the best efficiency and quieter cabin. The drag from open windows grows rapidly with speed and can overshadow the AC load for most vehicles.

Very hot or humid conditions

AC is the practical choice. Use “recirculate” to cool already-conditioned air and reduce compressor work. In stop-and-go heat, give AC priority over open windows to control humidity and prevent fatigue.

EV-specific considerations

Precondition the cabin while plugged in and use “Auto” or “Eco” climate modes. Ventilated seats and targeted cooling can keep you comfortable at slightly higher set temperatures, protecting range. At sustained highway speeds, windows up with efficient AC is usually best.

Practical ways to stay cool and save energy

These steps can help you maximize comfort while minimizing fuel or range penalties, whichever option you choose.

1. Pre-cool or pre-vent: If safe, open doors briefly or run the fan to purge hot air before setting off; EVs should precondition while plugged in.
2. Use recirculate in hot weather: It cools already-cooled cabin air, reducing compressor workload.
3. Set a moderate temperature: Aim for the lowest comfortable fan speed and a setpoint around 72–76°F rather than “LO.”
4. Close windows as speed rises: Enjoy fresh air at low speeds; switch to AC before highway pace.
5. Target the driver first: Use directional vents; in EVs, use seat or steering-wheel cooling/heating if available.
6. Manage solar load: Park in shade, use sunshades, and consider legal window tint to reduce heat gain.
7. Maintain the system: Keep the cabin filter clean and ensure AC service is up to date for peak efficiency.
8. Avoid long idling for cooling in gas cars: It wastes fuel; move air with the fan or get moving where AC is more efficient.

Applied together, these tactics narrow the efficiency gap between windows and AC, letting you choose based on comfort without a major penalty.

Safety, comfort, and noise

Windows down increases cabin noise and can cause buffeting, which is tiring on long drives; AC keeps the cabin quieter and maintains better filtration in dusty or high-pollen areas. In rain or on debris-strewn roads, windows up and AC on “recirculate” improves visibility and air quality. Balance efficiency with alertness and comfort—both matter for safe driving.

Bottom line

Below about 40 mph, windows down is usually more efficient if conditions are mild. From roughly 45–50 mph and up, AC with the windows up typically uses less energy than the drag penalty of open windows. In high heat or humidity—or for allergy and air-quality reasons—choose AC and use recirculate. EV drivers should precondition while plugged in and rely on efficient climate modes and targeted cooling to protect range.

Summary

Choose based on speed and conditions: windows down at low speeds, AC at highway speeds, and AC in hot or humid weather. Use recirculate, moderate settings, and preconditioning (especially in EVs) to minimize the energy hit. Comfort and safety should guide the final call, with these tips helping keep the cost—and the range impact—down.

What is the $5000 AC rule?

The “$5000 rule” for HVAC systems is a guideline to help decide between repairing or replacing an air conditioner: Multiply the age of the unit in years by the estimated cost of the repair in dollars; if the total is greater than $5,000, replacement is likely the more cost-effective option, while a total under $5,000 suggests a repair is the better choice. This rule serves as a starting point, but other factors like the system’s overall condition, energy efficiency, warranty status, and your future housing plans should also be considered.
 
How to Use the $5000 Rule 

1. Determine the age of your AC unit: (e.g., 10 years old).
2. Get an estimate for the repair cost: from a qualified technician (e.g., $600).
3. Calculate the total: by multiplying the age by the repair cost (e.g., 10 years x $600 = $6,000).
4. Compare the total: to $5,000:
   • Total > $5,000: Replacement is likely the smarter choice.
   • Total < $5,000: Repair may be the better option.

Why the Rule Matters

• Cost-Effectiveness: It helps homeowners avoid spending more money on an old, failing unit by “throwing good money after bad”. 
• Clarity: It provides a straightforward framework to make a decision when faced with a costly repair. 
• Future Savings: Replacing an old unit with a new, more energy-efficient model can lead to significant savings on utility bills over time. 

Factors to Consider Beyond the $5000 Rule

• Energy Efficiency: Newer AC units are significantly more efficient, potentially lowering energy costs. 
• System Condition: A well-maintained older system may still have life left, while a system in rough shape might need replacement regardless of age. 
• Frequency of Repairs: Multiple recent repairs can indicate a trend of ongoing issues. 
• Warranty: Check if your unit is still under a manufacturer’s warranty, as this can significantly reduce repair costs. 
• Homeowner Plans: If you plan to sell your home soon, a new AC can be a selling point. 
• Refrigerant Type: If your system uses R-22 refrigerant (a phased-out, ozone-depleting chemical), repairs may become more expensive and parts harder to find. 

What uses more gas driving with AC or windows down?

While all this might seem like a minor issue, getting it wrong can have a notable impact on your fuel economy; using AC can increase your fuel consumption by as much as 10% but opening the windows at higher speeds can increase fuel consumption by as much as 20%.

Is it better to have windows down or AC MythBusters?

MythBusters found that at lower, urban speeds (like 45 mph), running the air conditioner is less fuel-efficient than having the windows down, as the drag from the open windows has less of a negative impact at slower speeds compared to the engine load from the AC. At highway speeds, however, the opposite is true: the drag from open windows significantly increases and outweighs the load of the air conditioner, making AC more fuel-efficient.
 
You can watch this video to see an overview of the MythBusters experiment: 34sxXMetalicDustXxYouTube · Mar 9, 2011
MythBusters’ Experiment and Findings 

• The Test: The MythBusters team used two identical SUVs, driving them at 45 mph until their fuel ran out.
• The Setup: One SUV had the windows rolled down and AC off, while the other had the windows up and AC on full.
• The Result: The SUV with the windows down ran significantly further than the one with the AC on, showing that at 45 mph, using the AC was less fuel-efficient.

Why the Difference at Different Speeds

• At Lower Speeds (City Driving): . Opens in new tabThe increase in aerodynamic drag from open windows is less significant, making the AC’s load on the engine the primary factor in fuel consumption. 
• At Higher Speeds (Highway Driving): . Opens in new tabThe aerodynamic drag from open windows dramatically increases, creating much more resistance and causing the engine to work harder, leading to greater fuel consumption than running the AC. 

The General Rule 

• Use the AC for highway speeds: to maintain better fuel efficiency.
• Roll down the windows: at city speeds or in stop-and-go traffic to conserve fuel.

Is driving with windows down bad for gas mileage?

Having your windows down wastes more gas than running the air conditioner at highway speeds (typically above 40-50 mph) due to increased aerodynamic drag, but it is more fuel-efficient at lower, city-like speeds where the load on the engine from the A/C is more significant than the minimal drag from open windows. 
Why wind resistance matters

• Aerodynamic Drag: . Opens in new tabAt higher speeds, open windows create significant air resistance, or drag, making the engine work harder to maintain speed and consume more fuel. 
• Engine Strain: . Opens in new tabWhile modern A/C systems are efficient, the added load on the engine by the A/C compressor at lower speeds can consume more fuel than the drag from open windows. 

When to choose open windows vs. A/C

• Lower Speeds (City Driving): . Opens in new tabRoll down your windows for better fuel efficiency. The drag from open windows is minimal at these speeds, and the A/C’s strain on the engine can be more costly. 
• Higher Speeds (Highway Driving): . Opens in new tabUse the air conditioning with the windows up. The significant drag from open windows at these higher speeds increases fuel consumption much more than the load from the A/C system. 

In summary 

• Low speeds: Open windows are generally more fuel-efficient.
• High speeds: Use the air conditioning for better gas mileage.