In most American states, the kilowatt-hour cost of electricity ranges from about 6.35 to 13.17 cents and is substantially more in California and the Northeastern coastal states, according to estimates from All Systems Mechanical. While it's easy to not worry about a few cents at a time, those pennies add up over the hours, days and months you run your air conditioner.
Among other variables, your window unit's British Thermal Unit-based cooling power affects how much juice it uses, which in turn affects how much it costs to run. BTUs represent the amount of energy required to run the AC; one BTU is the amount of energy required to cool one pound of water by 1 degree Fahrenheit. Luckily, you won't have to break out a water bucket or a thermometer to figure out your own home's cooling cost; you'll just need to know its basic specs.
TL;DR (Too Long; Didn't Read)
In order to calculate the operating cost of your window AC unit, you will need to know the wattage uses by your unit and the total cost per kilowatt hour charged by your utility company.
Understanding The Formula
To figure out how much it costs to operate your window-unit AC, you'll first need to know how many amps it draws. This info should be readily available via the unit's physical or online spec sheet. For an 8,000-BTU AC, this figure often hovers around 6.0 amps.
Once you have the amps, multiply that figure by the voltage of your AC (also available on the spec sheet) to figure out the wattage it uses. For a window unit, the voltage is usually 110 volts. For a 6-amp AC at 110 volts, your formula looks like this: 6 amps x 110 volts = 660 watts. Now, divide that sum by 1,000 to get the kilowatt hours for your air conditioner. In this case, the kilowatt hours equal 0.66.
Finally, it's time to break out your last electric bill to find out how much your utility company charges per kilowatt hour. Multiply the cost in cents by the kilowatt-hour sum (0.66, in the example) to estimate how much your window unit costs per hour to run.
Evaluating Cost Estimates
If you'd rather not do the math yourself, Silicon Valley Power of Santa Clarita saves you some work and chimes in with the estimated costs of running an 8,000-BTU window unit AC. At 120 volts, the AC costs roughly $0.08 per hour. If your AC runs for eight hours a day during seven months of the year, that's about $134.40 annually.
Cutting Your Costs
No matter how much your window unit costs to run, you don't have to be held hostage to a utility bill. More efficient cooling habits will not only save you some coins, but they're better for the environment too.
Shading your home with trees keeps your home naturally cooler, and shading the AC itself with greenery can increase its efficiency by up to 10 percent. You can also make sure your window unit is operating at maximum efficiency – which also makes for maximum cost efficiency – by keeping its filter clean and fresh.
Don't neglect lo-fi methods like window covers and ceiling fans, either. Solar screens intercept up to 70 percent of warm solar energy, and using fans to lower your home's temperature by just 2 degrees Fahrenheit can cut your cooling costs by up to 14 percent.
- 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.
Dan's decade-long experience as a freelance writer and small business owner has seen him contribute to financial publications including Chron.com, Zacks.com, MSN Money, Fortune, Motley Fool and others.