AC Wattage & Sizing Calculator
Determine the cooling capacity and electrical power consumption for your room.
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How to Calculate Air Conditioner Wattage
Understanding the wattage of an air conditioner is crucial for two reasons: ensuring your electrical circuit can handle the load and estimating your monthly utility bills. The power consumption of an AC unit is directly tied to its cooling capacity, measured in British Thermal Units (BTUs).
The BTU to Wattage Relationship
The relationship between cooling capacity (BTU) and electrical power (Watts) is defined by the Energy Efficiency Ratio (EER). The formula is simple:
Wattage = BTU / EER
A higher EER rating signifies a more efficient unit. For instance, a 10,000 BTU unit with an EER of 10 will consume 1,000 watts, while the same unit with an EER of 12 would only consume 833 watts.
Key Factors Affecting AC Requirements
- Room Square Footage: The primary driver. Generally, 20 BTUs are required per square foot of living space.
- Occupancy: Humans radiate heat. If more than two people regularly occupy the room, add 600 BTUs for each additional person.
- Sunlight Exposure: If the room is exceptionally sunny, increase the capacity by 10%. If it is heavily shaded, reduce it by 10%.
- Kitchen Heat: If the unit is cooling a kitchen, the heat from appliances requires an additional 4,000 BTUs of cooling power.
Real-World Example Calculation
Imagine a 400 sq. ft. living room with normal sunlight and 2 occupants, using a unit with an EER of 10:
- Base BTU: 400 sq. ft. × 20 = 8,000 BTU
- Adjustments: None (Normal sun, 2 occupants)
- Wattage: 8,000 / 10 = 800 Watts
- Current Draw: 800W / 120V = 6.67 Amps
Why Energy Efficiency Matters
Choosing a unit with a higher EER or SEER rating might cost more upfront but saves significant money over the lifespan of the appliance. Modern inverter-based ACs can dynamically adjust their wattage, often running at much lower power levels once the target temperature is reached, unlike traditional fixed-speed compressors that are either 100% on or completely off.