How Much Will It Cost Me to Run an Air Conditioner?

Programmable thermostats can save you hundreds in heating and cooling costs.

Programmable thermostats can save you hundreds in heating and cooling costs.

When the thermometer rises in the summer, the cost of turning on an air conditioner may seem minor compared to getting some relief from the heat — but knowing how much air conditioning costs and how you can reduce that cost makes good fiscal sense. According to the Energy Information Administration, Americans spend more money cooling their homes than any other single usage of electricity, accounting for 22.4 percent of the average household electric bill in 2010.

Typical Electricity Costs

The town of Wellesley, Mass., has estimated the average cost of running central air conditioning in a typical home for six hours a day will use 900 kilowatt/hours (kWh) per month. At a cost of $0.134 per kWh, this amounts to $120.60 per month. A large 12,000 BTU air conditioner, like that in a window, running six hours each day will consume 270 kWh, at a cost of $36.26 per month. A smaller 6,500 BTU room air conditioner will consume 144 kWh at a cost of $19.34 per month.

Understanding Kilowatt-Hours

The kilowatt-hour (kWh) is the standard unit of measurement for electricity in the United States. This is 1,000 watts of electricity being used for one hour. To calculate how much your air conditioner costs to run for an hour, look for its wattage on the box or in the instruction manual and multiply this by the number of hours you use it each day. For example, a 1,000-watt air conditioner running for one hour consumes 1 kWh. By comparison, a 60-watt light bulb running for an hour uses 0.06 kWh (60 watts divided by 1,000). The cost of electricity varies by region. While the average cost in the US in 2011 was 12 cents per kWh, it was as high as 33 cents in Hawaii and as low as 8 cents in Idaho. Check your electric bill to determine your cost.

Air Conditioner Size and BTUs

The size of air conditioner you should purchase depends on the size of the rooms it will be cooling, how well your house is insulated, and whether or not the rooms are facing direct sunlight. An air conditioner's ability to cool is measured in British Thermal Units (BTUs). For example, to cool a 100- to 150-square-foot room that is well insulated and not facing direct sunlight, you need about 6,600 BTUs, which requires about 1,934 watts. The same room in direct sunlight requires about 7,260 BTUs, using 2,128 watts. A poorly insulated room in direct sunlight needs about 9240 BTUs, using 2708 watts.

Cutting Costs

A programmable thermostat can reduce the cost of central air conditioning if you program it at a higher temperature while you are at work and while you are sleeping. The temperature you set the air conditioning at should be relative to the outside temperature. If the temperature outside is 90 degrees, setting the air conditioning to 78 should feel quite comfortable in comparison. Drawing the blinds during the day and opening windows at night when it is cool can also save you money. When purchasing an air conditioner, look for Energy Star units, which use up to 14 percent less energy than government requirements and may entitle you to a tax credit of up to 30 percent of its cost.

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