You know that turning on the window air conditioner will increase your electric power bill. I would be helpful for both your peace of mind and budget planning to know how much it actually costs to cool your home. With the BTU rating of your air conditioner in hand, you can calculate the hourly, daily and monthly cost of cooling your home.

### Items you will need

- Recent electric bill

Look up your cost of electricity per kilowatt-hour from a recent power bill. The cost is described in cents per kilowatt-hour. Most power companies charge for electricity in tiers. The more electricity you use, the more it costs. Running the air conditioner will add to your power usage and the additional use will be charged at your highest tier rate. Review your bill for the most expensive per hour rate you were charged.

Look up or estimate the energy efficiency rating -- EER -- of your room air conditioner. If your unit is new, the EER should be listed on the included paperwork. If you need to estimate, use an EER of 8 for a relatively new A/C unit and an EER of 5 if the air conditioner is an old clunker which has been hanging in the window for years.

Divide the 8,000 BTU cooling capacity by the EER to determine the power consumption in watts per hour of the air conditioner. For example, if you have an A/C unit with an EER of 8, divide 8,000 by 8 to get a power consumption of 1,000 watts per hour -- or one kilowatt per hour.

Multiply the air conditioner power consumption per hour times the number of hours the unit runs per day to determine the daily power usage by the air conditioner. If the air conditioner is used 10 hours per day, the daily power usage is 10 kilowatt-hours per day.

Multiply the kilowatt-hours used per day times the electricity rate charged by the power company. If you use 10 kilowatt-hours daily and the highest-tier rate you pay is 20 cents, the air conditioner costs $2.00 per day, or about $60 per month.

#### Tips

- The most important factor in the calculation is to determine your top-tier cost for electricity. Cooling your home requires additional power above your normal electricity usage. The top-tier rate may be two to three times the rate you pay for the first kilowatt-hours of power used each month.
- Appliance industry standards require new window air conditioners to have an EER of 8 or higher. If you have a newer unit, your air conditioner is at least this efficient. If it is more efficient, your power usage cost will be lower than calculated.

#### References

#### Photo Credits

- Jupiterimages/Photos.com/Getty Images

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