EER, ISEER, COP, And BEE Star Rating: Understanding AC Efficiency Terms

When we go to the market to buy an AC, what is the first thing we consider? The BEE star rating. Right? If the star rating is high, the AC will consume less electricity and vice versa. This is a general perception, and that is true also.

The government has made it mandatory for all AC and Refrigerator manufacturers to show a BEE star rating on all air conditioners and refrigerators to get an idea of how much power that particular appliance is going to consume. So basically, star rating says how efficient your AC or refrigerator is in terms of power consumption.

But do you know that there are so many other efficient terms printed on the same star rating label, and you are not aware of that, like EER, ISEER, COP, etc.? Understanding those terms is equally important to make a proper purchase decision.

For a general consumer, knowing about all those technical terms may not be that important. But when you are spending your hard-earned money on Appliances, it is not bad to buy the best appliances by knowing about those technical terms of AC and refrigerator.

So in this article, we will talk about a BEE star rating, EER, ISEER, COP, and the key differences between all those terms. But before that, we should know what is meant by efficiency.

What Is Efficiency?

The efficiency of a product is the ratio of output to input. For a given input, if the output is more, the efficiency will be more. On the other hand, if the output is less at a given input, that means the efficiency is less.

What Is BTU ( British Thermal Unit)?

BTU ( British thermal unit)is an international standard of energy used to measure the amount of heat required to raise one pound of water temperature by one degree Fahrenheit.

In AC and Refrigerator, BTU means the amount of heat that it can remove per hour. So if the BTU value is more, it can remove more heat and vice versa.

For example, if you have 15×10 feet room, you may need an AC with 5400 BTU, if you have a 10×20 feet room, then you may need a 6000 BTU AC. So if your room sizes increase, you need an AC with a higher BTU.

What Is Tonnage Of AC?

The cooling capacity of AC is measured in Tons. You might have heard about 1 ton AC, 2 ton AC when you shop around for an AC. Right? That is the cooling capacity that we measure in Ton.

In other words, 1 ton of AC can give you the same amount of cooling per hour that one ton of ice can give if you keep that much ice in a room. 1 ton AC is capable of removing 12000 BTU heat from a room.

Here is a simple chart showing the room size and an approximate tonnage value of an AC.

Room Size (SFT-Square Feet)Recommended AC Size
Up to 80 SFT0.75 Ton
80-120 SFT1 Ton
120-180 SFT1.5 Ton
180-300 SFT2 Ton

EER (Energy Efficiency Ratio)

EER stands for Energy Efficiency Ratio, which is equal to the amount of heat removed per hour divided by the electricity consumption by the air conditioner. Also, in other words, EER is the ratio of cooling competence in BTU per hour to the power input in watt.

Lets me explain with an example. If one 10,000 BTU air conditioner uses 1000 watts of power, then the EER rating would be 10, calculated by dividing 10,000 to 1000 (10,000/1000=10).

If the same AC ( 10000 BTU) consumes 1200 watts of power per hour, then the EER would be 10000/1200)= 8.33. So now you have understood that higher EER means more energy efficiency like BEE Star ratings.

Manufacturers no longer show EER values on their AC. Instead, they show the ISEER value. We will learn the reason for that later in this article. So ideally, EER now just a theoretical term.

Here is the relation between the EER and star rating until 2019.

bee star rating
EER Rating

SEER ( Seasonal Energy Efficiency Ratio)

SEER or Seasonal Energy Efficiency Ratio is similar to EER, but the only thing is that it consider seasonal variation as a factor. The reason is that in India, the season is not the same all across the country.

For example, in Delhi, for a room having 10X15 size, you may need 1 ton AC. But if you want to cool the same room in Himachal, you may need just a 0.5 ton AC. So seasonal variation is significant.

That is why SEER adds a seasonal factor into the EER to calculate the SEER value. That factor value can be 0.5, 0.75,1,2, or anything depending on the season of that location.

SEER values are no longer shown on AC labels as it is replaced by ISEER rating.

ISEER ( Indian Seasonal Energy Efficiency Ratio)

ISEER is the Ratio of the total annual amount of heat that an AC or Refrigerator can remove from the indoor air when operated for cooling in active mode to the total annual amount of energy consumed by the equipment during the same period.

The concept of EER, SEER and ISEER is the same. But ISEER considers two factors as shown below.

  • CSEC
  • CSTL


CSEC (Cooling Seasonal Energy Consumption)

CESC is the total amount of energy consumption by the AC or Refrigerator per year when it is active, regardless of the cooling procedure.

CSTL ( Cooling Seasonal Total Load)

CSTL is the total amount of heat load that is removed by an AC or refrigerator per year when it is active, regardless of the cooling procedure.

The ISEER value printed on your AC box assumes that you will run the AC for 1600 hours per year. If you use the AC for more hours, then the efficiency may vary.

CoP (Coefficient Of Performance)

The coP is the ratio of the amount of cooling provided by an AC to the energy it consumes. So if the CoP is 1, then the AC will be 100% efficient.

We know that 1 KWH= 3412 BTU
1W= 3.412 BTU/Hr

Now let’s go to the formula of EER

EER= (BTU/hr)/ W= (BTU/Hr)/( 3.412 BTU/hr)= 3.412 CoP

So EER= 3.412 CoP

BEE Star Rating

Whatever we discussed till now does not make any sense for general consumers to be very frank. What is matters is the star rating. If the BEE star rating is high, the machine is more energy-efficient. In India, the star rating and ISEER value are interconnected. What that means is that if the ISEER value is more, the star rating value will also be high.

bee star rating

Here is the relation between ISEER and star rating in the India market.

Star RatingMinimum ISEERMaximum ISEER
Effective from January 2021 to December 2023

Conclusion: BEE Star Rating

So now you all might have got an idea about different technical terms of AC. So next time when you buy an AC or Refrigerator, make sure you see the value of all those efficiency terms and then only take a decision. In that way, you will be saved from buying the wrong product.

If you still have any questions or queries, please write in the comment section, and I will be happy to assist.

You may also like to read: AC Buying guide


Rajib is the Co-Founder and the Lead Product Analyst of RiansTech. A BTech in Mechanical Engineering and a veteran in the Home Appliance industry with over 17 years of experience in designing appliances for industry leaders like GE and Whirlpool. He also runs a successful niche blog (RiansClub) on Mechanical Engineering

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