SEER rating tells how much heat (BTU) can an air conditioner remove out of the house per watt of electricity it uses. Higher SEER rating equals higher efficiency of the air conditioner.

SEER ratings help when comparing two or more air conditioners. The higher SEER the more efficient the air conditioner. The spreadsheet below shows cost of air conditioning with different SEER rating.

The cost of electricity is assumed 6 c/kW. The amount of heat produced by different physical objects is in BTU/hr. All the numbers are approximate.

A human body:
-Resting – 350
-Hard Working – 2,000

A regular 100 W bulb – 340

A kitchen stove:
– A small burner – 5,000
– A Large burner – 20,000
– An oven – 20,000

A computer – 1000

Example 1

The size of your air conditioner is 1 ton. How much does it cost you to run your air conditioner for 1 hour?
One ton of cooling is 12,000 BTU/h. After we enter 12000 into the spreadsheet, it returns us the cost 9 cents an hour for an old 8 SEER air conditioner and 5.14 cent for a Energy Star 14 SEER air conditioner.

Example 2

A 3 ton air conditioner runs on average half of the time around the clock. How much electricity does it use?
Since one ton of cooling removes 12,000 BTU/h of heat, we enter 12,000×3=36,000 into the spreadsheet. It returns 27 cents an hour for the old air conditioner, 13.5 for the new and 15.43 for a mainstream 14 SEER unit. With this numbers the old unit costs $0.27x24x0.5=$3.24 a day to run. The 16 SEER unit costs $1.62 and the 14 SEER unit costs $1.85 a day to run.

Example 3

You are planning a party for 10 people. The party will last 4 hours with some activities, like dancing – 800 BTU/h per person. Total 800 x 10 x 4 = 32,000 BTU One hour of cooking will precede the party. Oven and 2 large burners will produce 20,000 x 3 = 60,000 BTU. All the extra heat in the house will total 92,000 BTU.

Cost of cooling is 69 cents with an old air conditioner and 39.4 cents with 14 SEER new one. Perhaps you can afford cooling of your party if you can afford the party itself.

One more consideration though.

While cooking you will need 60,000 BTU/h EXTRA cooling capacity, and this is 5 ton of cooling – the size of the biggest residential unit on the market. You do not have that much EXTRA cooling available. The most effective way to fight cooking heat and moisture would be using of the kitchen exhaust fan.

Extra heat from 10 people will require less than 1 ton of cooling . Most probably your air conditioner will be able to handle it if it’s not too busy fighting sun load.

Now you are ready to play with numbers yourself.

ARI Reference Number
Replacing Air Conditioner
Cost of Air Conditioning