Comparison: central air, window AC, portable AC, and fans
Energy Consumption
The amount of electricity a cooling device uses depends on its power rating and how long it operates. Watts (W) measure the rate of electricity use, while kilowatt-hours (kWh) measure the amount of electricity consumed over time.
Typical power ranges include:
Central air conditioning: A central AC system can draw several thousand watts while the compressor and blower are running. A figure such as 3,500 watts (3.5 kW) may be reasonable for some systems, but actual power consumption varies considerably by system size, efficiency, operating conditions, and whether the compressor is running continuously.
Window air conditioner: Many window AC units draw roughly 600–1,500 watts, depending on their cooling capacity and efficiency. For example, current ENERGY STAR-certified window units range from relatively low-power models to substantially higher-power units as cooling capacity increases.
Ceiling fan: Typically uses approximately 30–50 watts, although actual consumption varies by fan size, motor, and speed setting.
Small box fan (≤10 inches): Often uses approximately 25–30 watts at higher speed settings, although the exact amount varies by model.
Large box fan (approximately 20 inches): Commonly uses around 50–100 watts, although some models can consume more depending on their motor and speed setting.
Important: These numbers represent approximate power draw, not daily electricity consumption. To estimate daily energy use, multiply the device's wattage by the number of hours it operates and divide by 1,000.
For example, a 50-watt fan running for 10 hours uses:
50 W × 10 hours ÷ 1,000 = 0.5 kWh
How Fans and Air Conditioners Cool You
Fans and air conditioners work in fundamentally different ways.
Fans do not actually lower the air temperature. Instead, they increase air movement across your skin, which accelerates the evaporation of sweat and can make you feel considerably cooler.
Air conditioners actually remove heat from indoor air. They use a refrigeration cycle to transfer heat from inside the building to the outdoors. As part of this process, conventional air conditioners also remove moisture from the air, which can make the indoor environment feel more comfortable.
Cooling Efficiency and Safety
Fans are generally much more energy-efficient than air conditioners because they use far less electricity. However, their cooling effect is primarily on people, not the room itself. A fan can make you feel cooler while the actual indoor temperature remains unchanged.
There are also limits to how effective fans are during extreme heat. The CDC warns that when temperatures reach the mid-90s or higher, electric fans will not prevent heat-related illness.
Therefore, when indoor temperatures become dangerously high, air conditioning or another method of actively lowering the indoor temperature is generally safer than relying on a fan alone. This is especially important for older adults, young children, and people who may be more vulnerable to heat.
It is also worth noting that there is no universal temperature such as exactly 90°F at which everyone must switch from a fan to air conditioning. Heat risk depends on factors including temperature, humidity, duration of exposure, age, physical activity, and individual vulnerability. The CDC's guidance specifically cautions that fans are not protective against heat-related illness at sufficiently high temperatures.
Your Indoor Temperature May Be Very Different From the Weather Report
The outdoor temperature reported by a weather service does not necessarily reflect the temperature inside your home. Indoor conditions can be affected by factors such as:
Building construction and insulation
Sun exposure and window orientation
Ventilation
Humidity
Number of occupants
Heat generated by appliances and electronics
Outdoor surroundings, including vegetation and paved surfaces
Location and floor of the building
During a heat wave, your safety should always come first. A fan may be an inexpensive and energy-efficient way to improve comfort, but it should not be relied upon as the sole cooling strategy when indoor temperatures become dangerously high.
Stay cool, drink fluids regularly, limit strenuous activity during extreme heat, and use air conditioning or seek a cooler location when necessary.
Sources
Centers for Disease Control and Prevention (CDC). Climate Change and Extreme Heat: What You Can Do to Prepare.
Centers for Disease Control and Prevention (CDC). Extreme Heat.
ENERGY STAR (U.S. Environmental Protection Agency). Room Air Conditioners: Key Product Criteria.
https://www.energystar.gov/products/room_air_conditioners/key_product_criteria
ENERGY STAR (U.S. Environmental Protection Agency). Certified Room Air Conditioners.
https://www.energystar.gov/productfinder/product/certified-room-air-conditioners/results