ISEER, EER, BEE Star Ratings – Understand Air Conditioner Jargon!

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There is an unwritten rule in marketing. “If you cannot convince anyone, ensure that you confuse them 😛 

Every business enterprise resorts to following this rule intentionally or unintentionally. Hence, you find manufacturers using different types of technical jargon while selling their products.

An overwhelming majority of people cannot make head or tail of what the manufacturer is trying to convey. This is an unpalatable fact. Whether you like it or not, it is, unfortunately, true most of the time.

We shall take the simple example of the ‘Star Ratings’ you see on electronic appliances such as the air conditioners. Honestly speaking, how many people understand the concepts like tonnage, BEE (Bureau of Energy Efficiency/ EER / ISEER Star Ratings, BTU, etc. This list can go on forever.

Hence, the Government has made it easy for people by stating that a higher star rating is always better than a lower star rating. 

It is with this limited knowledge that people venture to buy ACs.

This article will try to shed light on the aspects that govern these star ratings so that you go to the AC shop with some knowledge about how the system works. You might be able to ask questions. Let us now look at some of the jargon used by AC manufacturers.


You must have heard people use these words very often. ‘I have a 1.5-ton AC or a 1-ton AC in my house.”

What does this signify? Do you mean to say that the AC weighs 1 or 1.5 tons? In that case, your buildings will not be able to bear the load. 😛

In this context, we refer to the word ‘ton’ as the amount of heat removed by the air conditioner in one hour.

How do you measure heat? In India, you use the British system for measuring a lot of things. Heat is one of them. You measure the amount of heat removed in terms of British Thermal Units (BTU). Higher the BTU, higher will be the cooling capacity.

Definition of BTU

Let us look at the definition of BTU according to the mother of all sources, “Wikipedia.

BTU is the “amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit.” In simpler terms, we can say that 3,412 BTU = 1 Kw/hr

Coming back to the tonnage aspect, we can say that 1 ton = 12,000 BTU/hr. How did this term originate?

Historically speaking, a ton is the amount of space cooled by 1 ton (weight) of ice.

How do you choose the right tonnage for your air conditioner?

This is a million-dollar question. Frankly speaking, you do not have a universal answer to this question. It depends on a lot of variable factors such as the size of the room, number of people and appliances in the room, the city of usage, etc. It also depends on the season.

In the summer season, there is more heat. Hence, you require a higher tonnage. Similarly, during the day the heat is more as compared to the night. All these factors go into choosing the right kind of tonnage for the AC.

Air conditioner tonnage room size

Now, I think you are beginning to understand why the AC manufacturers try to confuse you instead of convincing you. However, you can deduce that you have to keep the peak summer season day in mind while choosing the right tonnage for the AC.

However, you have to note one point very carefully. If you have a room that needs about 1.2 tons of cooling, buying a 5-star 1.5 ton AC is not an advisable thing.

We mean to say that oversizing an AC can cause inefficiency.


We have taken care of the tonnage aspect. We move on to the next aspect i.e. efficiency.

What is efficiency?

In standard layman terms, efficiency is output divided by input. In other words, for a given input, the higher the output, the higher is the efficiency. When it comes to measuring the efficiency of air conditioners, you have to look into two aspects.

Energy Efficiency Ratio (EER)

You are going to hear a lot about this ratio, EER in this article. Hence, it is better to have a clear understanding. When you look closely at the “Power savings Guide” sticker on every appliance, you will come across this figure.

BEE Star label

In simple terms, EER is equal to the amount of heat removed per hour divided by the power consumed by the AC.

Therefore, EER = BTU/hr/Watt.

This entails that the higher the amount of heat removed by the AC per unit of electricity consumed, the higher is the efficiency. Therefore, air conditioners with higher EER are better.

Various factors go into the computation of the EER. However, the accepted norm is as follows. (35 degrees Celsius – Outdoor temperature, 27 degrees Celsius – Indoor temperature, Humidity – 50%)

Coefficient of Performance (COP):

This will be a unit-less ratio as all coefficients are. Prior to understanding what COP conveys, you should have an idea about the relationship between BTU and kW/hr. As explained earlier in the article, 1 KW = 3412 BTU/hr (1W = 3.412 BTU/hr).

Technically speaking COP of an air conditioner is equal to the ratio of the amount of heat removed per watt to the amount of power consumed per watt. If you combine both the concepts of COP and EER, you get the equation as follows.

EER = 3.412 COP

The star ratings of the AC units depend on the EER and the COP. These ratings change from time to time. The Bureau of Energy Efficiency (BEE), Department of Energy Saving, Government of India prescribes the star ratings based on the above ratios. As of date, the star ratings are as follows.

bee star ratings for air conditioner 2021, 2022 and 2023

The star ratings are over a range of EER. Hence, you should also look at the ISEER figure on the Star rating sticker while purchasing your split AC.

An ISEER of 3.8 is a 3-star AC whereas an  ISEER Value: 4.2 makes it a 5-star one. Automatically costs will vary. As a purchaser, you should note this fact very carefully.

Secondly, a 5-star AC is certainly more efficient than a 3-star one. It can save you electricity as well. On average, a 5-star AC can be around 15-20% more efficient than a 3-star AC. We are not comparing with the 1-star or 0-star ACs because no one actually buys them.

The Concept of SEER

The efficiency of the AC depends on the external temperature and the internal temperature. Now, the temperature is not the same throughout the year. In winters, the temperatures are significantly lower as compared to the summer months.

Secondly, the usage of the ACs in winters is less as compared to the summer usage. Hence, the concept of Seasonal Energy Efficiency Ratio (SEER) comes into the picture. You have this concept worldwide.

The ISEER Concept


When you use the SEER concept, you have to consider that the seasons can differ from country to country. Therefore, you have different SEER for different countries. In India, you have the Indian Seasonal Energy Efficiency Ratio (ISEER). Let us see how the ratio pans out and what the various terminologies used in this concept indicate.

The basic concepts of EER and ISEER are the same. The only difference is the seasonal factoring. However, we shall discuss the same to get a better understanding of the concept.

Cooling Seasonal Energy Consumption (CSEC)

This comprises of the total amount of energy consumed by the AC unit while it is in active mode.

Cooling Seasonal Total Load (CSTL)

This is a computation of the total amount of heat removed by the AC in the active mode.

Indian Seasonal Energy Efficiency Ratio (ISEER)


This is the ratio of the total amount of heat removed by the AC to the amount of energy consumed during the process.

Rated Cooling Capacity at 100% load

Fixed-speed air conditioners have fixed cooling capacities. If it is a 1.5-ton AC, the rated cooling capacity is 1.5 tons. However, in the case of inverter air conditioners, there is a concept of variable cooling capacity. A 1.5-ton inverter AC can have a varying tonnage ranging between 0.3 and 1.8 ton. However, the manufacturers market the AC as a 1.5 ton AC. This is the concept of marketing tonnage.

Rated Cooling Capacity at 50% load

The BEE has made it mandatory for the manufacturers to provide the power consumption at 50% capacity. However, this does not entail that it is the minimum cooling capacity. Hence, for the 1.5 ton AC in our example, this figure will come to 0.75 ton.

Maximum Cooling Capacity

As the name suggests, the figure in our example should come to 1.8 ton.

Rated Power Input at 100% load

This figure denotes the power consumption in Watts when the AC runs at 100% load.

Rated Power Input at 50% load

Naturally, this figure is the power consumption at 50% load.

Maximum Power Input

This is the figure that denotes the power consumption at the maximum load. In this case, it is power consumption when the AC works at a 1.8-ton capacity.

Cooling Seasonal Energy Consumption (CSEC)

As declared in the table above, this figure is taken as 1600 hours as a base. However, your actual number will depend on your usage as well as the temperature of your city.

Tips to share

We have seen the concept of inverter ACs and the power savings they can deliver. Everything boils down to the fact how you use the AC. The frequency of usage is very important. These are after all ‘Statistics’.

We shall share some important tips in connection with this article.

1. Selecting the right tonnage of the ACs is very important. If your room demands an AC of 1 ton capacity, buying a larger one is not only expensive but also uneconomical.

Thus, oversizing the AC is not advisable. Similarly, under-sizing the same is also not the right thing to do. You end up having lower performance.

2. Understand that the BEE star ratings change every two years or so. We have listed out the tables in this article. This will give you a fair idea as to when the present rating period ends. The ratings are usually different in the next cycle.

3. Check it out especially when you buy the ACs towards the early part of the new cycle. Manufacturers can try to pass off the equipment with a higher rating. This can have an effect on the price.

4. The ratings are for a range of ISEER. An ISEER of 3.29 and 3.30 does not make much of a difference as far as efficiency is concerned. However, the ratings change from Star-3 to Star-4.

This can increase the cost of the AC. Therefore it is very important for the customer to check out the EER along with the ratings.

5. Usually, the EER on the labels is given as Watt/Watt. However, you sometimes find the EER in BTU/hr/Watt on the internet. This should not confuse you as we have explained the same in detail in this article.

6. The maxim is “More stars – More cost”. At the same time, “More stars can also result in more savings of power.” Check it out before deciding to buy the AC. In the longer run, you can end up saving more on the operation cost as compared to what you have incurred on the capital cost.

The city factor is an important one. You might need a 1-ton AC for a room in Chennai but a 0.75-ton in neighboring Coimbatore. The climate of the city makes a difference.

Final Words

We have shared enough information about star ratings and how they calculate the same. This can equip you with the knowledge to question the manufacturer or the dealer to ensure you get the best deal.

This article can ensure one thing for you. No dealer or manufacturer will be able to confuse you with jargon. It does not matter if they cannot convince you, but they cannot confuse you either. That is a victory by itself. Maybe, you might end up confusing the dealer.

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