An air conditioner will take a longer time to cool a large room than it will to cool a small room. The longer the air conditioner is actively operational, the more power it uses; therefore, if you are using the air conditioner to cool a large space, it will cost more than if you use the air conditioner to cool a small space.
Air Conditioner Power Rating
Each air conditioner draws a certain amount of electric current while in operation. According to Watt's Law, power as measured in watts is equal to voltage multiplied by electric current as measured in amps. A unit that draws 12 amps while in operation will use less power over the same time as a unit that draws 15 amps. Since most electric bills are based on the amount of power used, the amount of current that an air conditioning unit draws is a factor in how much it costs to run the unit. If an air conditioner that draws 12 amps is plugged into a standard electrical outlet in North America, the formula works out to 120 volts x 12 amps = 1,440 watts.
Poorly insulated rooms will quickly lose heat in the winter as well as allow heat to come in during the summer. This may cause an air conditioner to run constantly. In contrast, a well-insulated room will keep cool air in and hot air out during the summer. This will allow the air conditioner to cool the room to the desired temperature, after which the air conditioner may be turned off. Using an air conditioner in a well insulated room will allow you to keep cooling costs down.
Cost Per kWh
Most households are billed for how much power that the household uses in a month. The billing unit that the electric utility company uses is the kilowatt-hour. A kilowatt-hour is equal to 1000 watts of power that are used within one hour's time. The formula for calculating how much it will cost to run an air conditioner is as follows: Total cost = (Number of hours you will run the air conditioner x Air conditioner power) / Cost per kilowatt-hour. Therefore, if you intend to run a 1,400 watt air conditioner for 2 hours and your cost per kilowatt-hour is $0.10, the total cost to run the air conditioner for that time is $0.28.