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How To Calculate The Cost to Run an Air Conditioner

This section is on how to calculate the cost to run an air conditioner quickly using a rule-of-thumb method.  If you want to know the exact amount that you are paying for your air conditioner, breeze through this and then go to the next section.

Step 1 – Calculate the Amps Drawn by Your Air Conditioner

This part will vary greatly based on what the SEER rating of your unit is (see: SEER vs EER), and its size and manufacturer, so I will re-emphasize that this is a quick, layman’s guide to calculating the cost of running your air conditioner.  For this guide, the average amps drawn by a modern air conditioner is illustrated below and based on a SEER-16 rating (average air conditioner):

  • 2-Ton Air Conditioner – 15 amps
  • 3-Ton Air Conditioner – 18 amps
  • 4-Ton Air Conditioner – 21 amps

Write this down because you will need it in later steps.

Step 2 – Calculate the Wattage Used by Your Air Conditioner, Followed by Kilowatt-Hours

The calculation for figuring out the cost of running an air conditioner includes the number of Watts that you use as well.  To figure this out, simply multiply the amps from step 1 by the voltage of your outlet.  For this general price estimate, we will use a standard 240 volt power outlet which is the average size for a central air conditioner.  If you have a window air conditioner, then use 110 volts.

For instance, a 3-ton central air conditioning unit would look something like this:

18 amps X 240 = 4,320 Watts

To calculate Kilowatt-Hours, divide the number that you just calculated by 1,000 to find out one Kilowatt-Hour for your air conditioner:

4,320 Watts / 1,000 = 4.32 Kilowatt-Hours

Step 3 – Find the Average Price per Kilowatt-Hour for Your Region

Take a look at the graph below and figure out the average cost per Kilowatt-Hour based on your geographical region:

For our example today, we will use Santa Clarita, California which would have an average cost per Kilowatt-Hour of 14.37 cents.  Next, multiply the Kilowatt-Hours found in step 2 by this price to find out how much it costs to run your air conditioner for one hour.  Then multiply it by 24 to find out how much it costs for a day, and then by 30 to find out how much it costs to run your air conditioner for a month.

4.32 X 14.37 = 62 cents an hour,

62 X 24 = $14.89 per day,

$14.89 X 30 = $446.96 per month,

But wait!  That is way more than how much I pay for my entire electric bill each month!  How is this possible?  That is because this is the price of running your air conditioner continuously for a month.

Step 4 – Find Your Multiplier

Like I said in step 3, you have just figured out the cost to run an air conditioner for a given period of time non-stop, but your air conditioner doesn’t run all of the time!  It only runs when the temperature on the thermostat goes above the temperature you have set.  In fact, if you were to set your thermostat for 100 degrees then your cost for air conditioning would be $0, because your air conditioner would never run.  As such, the following multipliers can be used.  There is no exact way to calculate the proper multiplier and this is where the equation kind of starts to break down a bit.  Every day has a different outside air temperature, humidity level, etc.

However as a general guide, you can use the following multipliers based on an indoor household temperature of 70 degrees Fahrenheit, a properly sized air conditioner, and based on the assumption that the temperature drops 20 degrees at night:

Average Outside Daytime Air Temperature – Multiplier

  • 110 degrees – 0.8
  • 100 degrees – 0.4
  • 90 degrees – 0.3
  • 80 degrees – 0.25

The purpose of the multiplier is to estimate how often your unit is actually running.  For our example, we will use an average outside air temperature of 100 degrees (standard for a Santa Clarita summer):

$446.96 X 0.4 = $178.8 a month for a 3-ton unit.

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