A standard air conditioning system uses about 3,500 watts, according to the Otter Tail Power Company of Minnesota. At a usage of 860 hours during the cooling season, or summer, that's just over 1,000 kilowatt-hours of usage per month. This translates to a monthly cost of about $116 as of 2011.
Otter Tail bases its figures on a 2.5-ton air conditioning unit, which is suitable for a home up to 1,200 sq. ft. If your home is larger than 1,200 sq. ft., your monthly cost for air conditioning may be higher. If it's smaller than 1,000 sq. ft., it may be lower; it largely depends on how much you use air conditioning. If the temperature is moderate year-round where you live, you may use it less than Otter Tail estimates.
Central Air vs. Ceiling Fans
Ceiling fans and portable fans use between 65 and 250 watts, which is, at most, 7 percent of the wattage an air conditioner requires. If you left a fan on 24 hours a day for three months, it would only cost you $16 to $63 total. The major drawback is that a fan doesn't chill air as a central air conditioner does.
Getting the Most Value
For the most value, money management software company Money Allocator suggests setting the thermostat no lower than 78 degrees. Turn on a fan to circulate air throughout the room, and you can keep your home at a relatively comfortable temperature.