What is ISEER and Star Rating of ACs?


As per the statistics of the Bureau of Energy Efficiency (BEE), energy efficient electrical appliances have helped India in saving 140.54 BU (Billion Units of electricity) since 2011.

In the last year (2018-19) alone, India saved close to 20 BU (Billion Units).

Air Conditioners consume a lot of electricity and that is why most people shy away from using them.

With the objective of improving the energy efficiency of room air conditioners and promoting the manufacturing of energy efficient ACs, BEE has brought in star labeling of ACs.

In January 2009, BEE made the star-labeling of all room air conditioners mandatory. And ever since then no brand can sell any room air conditioner without a star label.

Mandatory BEE Star-Labelling Dates of Different Types of Air Conditioners

AC TypeMandatory Date
Room Air Conditioners (Window & 1:1 high wall split)January 2009
Ceiling Mounted Air ConditionersJanuary 2016
Room Air Conditioner (Variable Speed)January 2018

The star rating standards are continuously upgraded by BEE to progressively improve the energy efficiency of the appliances. This is evident from the fact that, if you had bought a 5-star rated split AC in 2010 then this AC is only as efficient as a 1-star rated split AC of 2018.

So what are these star ratings of AC and how are these calculated?

The ISEER rating is somewhat a new concept and not all the customers know about it. If you are new to this concept, it’s for you to pack yourself with the knowledge of BEE star rating and ISEER ratings. But before we shift our focus to ISEER rating for AC, we should first know about star ratings in AC.

What is Star Rating of ACs?

The Bureau of Energy Efficiency (BEE) has developed a grading system known as Energy Efficiency Ratio (EER). Most of the home appliances and electrical equipment comes with BEE star rating. The star ratings in AC tells you how efficient your air conditioner is. The higher the stars, the more energy efficient your AC is.

Bureau of Energy Efficiency, India, defines “Energy Efficiency Ratio” as the ratio of capacity (in Watts) to the power consumption at nominal voltage and frequency.

In simple terms, what this means is, EER is equal to the amount of heat removed per hour divided by the power consumed by the air conditioner. It merely means higher the heat removing capacity of the AC; higher is the star rating of the AC.

EER = Output Wattage (Cooling Capacity) / Input Wattage

For measuring the EER, a standard scenario is considered. BEE defined some standard test conditions for calculating the EER ratings which are as given below:

Relative humidity: 50%
Indoor temperature: 27 degrees Celsius
Outdoor temperature: 35 degrees Celsius

The EER ratings do not give you exact electrical units your air conditioner will consumer, but it provides you good means of comparing the electrical efficiency of two air conditioners.

EER ratings were ideally meant for fixed speed air conditioners. And the standard works well only when there is fixed input wattage and fixed output wattage.

After the launch of variable speed Inverter ACs, it became very difficult to find the energy efficiency ratings.

This was so because, both the fixed speed ACs and Inverter ACs cool differently. While fixed Speed ACs have fixed cooling capacity (or tonnage) and fixed input wattage, Inverter ACs have the varying cooling capacity and input wattage.

EER rating is also not a reliable benchmark for measuring the efficiency of AC during the non-peak cooling time.

Because of these limitations, it was eventually realized that EER even though it tells the customers about the efficiency of the air conditioners, it is not a reliable benchmark for measuring the efficiency of AC.

To overcome this problem, BEE has introduced the concept of Indian Seasonal Energy Efficient Ratio (ISSER).

Now that we know about star ratings of ACs, let us now look at what exactly is ISEER and how it is different from EER.

What is ISEER Rating for AC?

The ISEER has borrowed its concept from the Seasonal Energy Efficiency Ratio (SEER). The efficiency of your air conditioner depends both on the external and internal temperature. And we all know that the temperature varies throughout the year and this is why the EER rating is not enough to measure the actual efficiency. It is then the concept of SEER seeps in which considers the efficiency of the AC by taking into consideration the seasonal variations.

Now seasons can differ from one country to another, right? So, the SEER values of different countries is different. In India, we have the Indian Seasonal Energy Efficiency Ratio (ISEER).

Let us first understand some basic definitions:

Cooling Seasonal Energy Consumption (CSEC)” means the total annual amount of energy consumed by the equipment when it is operated for cooling in active mode;

Cooling Seasonal Total Load (CSTL)” means the total annual amount of heat that is removed from the indoor air when the equipment is operated for cooling in active mode.

Indian Seasonal Energy Efficiency Ratio (ISEER)” means the ratio of the total annual amount of heat that the equipment may 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;

ISEER = CSTL / CSEC

The ISEER rating tells you how much energy will be consumed by the air conditioner when it is used annually by taking into consideration the seasonal changes in the country.

The ISEER calculations are based on the bin hours of the national climatic zone, bin temperature range of 24°C to 43°C and 1600 operating hours per year. Annual temperature profile used is based on weather profile for 54 cities across India.

Below is the temperature distribution used:

Indian Outdoor Temperature Bin Distribution

Once ISEER is calculated, the value of the ISEER will decide the star rating as per the tables given below.

ISEER Star Rating Plan for Window Air Conditioners from 1st Jan, 2018 to 31st Dec, 2019

Star LevelMinimum ISEERMaximum ISEER
1 Star2.52.69
2 Star2.72.89
3 Star2.93.09
4 Star3.13.29
5 Star3.3 

ISEER Star Rating Plan for Split Air Conditioners from 1st Jan, 2018 to 31st Dec, 2019

Star LevelMinimum ISEERMaximum ISEER
1 Star3.13.29
2 Star3.33.49
3 Star3.53.99
4 Star4.04.49
5 Star4.5 

If you compare the above tables, you will understand the difference between the energy efficiency of window and split air conditioners. The energy efficiency of split air conditioners is high and so are the ISEER ratings.

An ISEER rating of 3.3 or more qualifies as a 5-star AC in the window type ACs and an ISEER of 4.5 or more qualifies as a 5-star AC in the split type ACs.

Understanding the BEE Star Label on AC

As per the mandatory guidelines of the Bureau of Energy Efficiency, every room air conditioner should have a BEE star label that displays the following details:-

  • type of air conditioner
  • the name of manufacturer or importer and brand
  • the model and year of manufacturing or import
  • cooling capacity (hundred percent) in Watts
  • cooling capacity (fifty percent) in Watts
  • electricity consumption in units per year
  • variable speed compressor
  • heat pump (yes/no)
  • Indian seasonal energy efficiency ratio
  • label period
  • star level

Below is a sample of a star rating label.

ISEER Star Rating Label

3-Star AC or 5-Star AC – What Should You Buy?

Ok, you understood the importance of BEE star-label and why you should buy higher star-rating air conditioners.

But should you buy a 3-star rated AC or a 5-star rated AC?

3 Star AC Vs 5 Star AC

The answer to your query is quite simple, you should always buy the highest star-rated AC. You should definitely buy a 5-star rated AC if you have the budget to invest in a 5-star rated AC.

A 3-star window AC has an ISEER that ranges between 2.9 to 3.09 and a 5-star window AC has an ISEER of 3.3 or above.

Let’s assume that the monthly electricity bill of your home with a 3-star window AC is Rs. 2,320, keeping all variables constant, a 5-star window AC would lower down your bill to Rs. 2,000. Considering you use the AC for 7 months in a year, you could potentially save Rs. 2,240 every year and Rs. 11,200 over a period of 5-years. Therefore, the total cost of ownership of a 5-star AC is lower in the long run as compared to that of a 3-star AC.

Energy Saving Comparison of Different Star Rated ACs

Note – Above calculations are based on an assumption that the AC runs 8 hours/day and the electricity cost is Rs. 7/unit. The actual operating cost will vary depending on factors like the room temperature and AC settings.

But if you are looking for an affordable option or if the AC is not going to be used regularly then a 3-star rated AC would be a good choice.

We do not recommend buying any air conditioner below 3-star rating as you will ultimately end up spending more than what you would have saved initially.

What is India Buying?

Let’s look at the AC manufacturing data of 2018-19 for finding an answer to what India is buying.

Star-Label Wise Air Conditioners Manufactured in India in Financial Year 2018-2019

Air Conditioners Manufactured 2018-2019

As you can see in the table above, the 3-Star rated ACs were manufactured in the highest numbers. Whether it is the Inverter AC or non-inverter AC, 3-Star rated ACs have clearly emerged as the preferred choice of most AC buyers in India.

We believe the price difference between a 3-star rated AC and a 5-star rated AC is the main reason behind this trend.

While 5-Star rated ACs offer the maximum energy efficiency and are slightly more expensive, 3-Star rated ACs offer the perfect combo of affordable prices and considerable power savings.

Things to Consider Before Buying an Air Conditioner

First of all, on the basis of the size of the room, you have to choose the right tonnage of the air conditioner. Suppose, your room needs an air conditioner of 1-ton capacity, and you end up buying a 1.5-ton capacity AC, then the air conditioner will prove to be not only uneconomical but also very expensive. Thus, oversizing and under sizing of the AC is not the right thing to do. If you buy an undersized AC then you will not get the expected cooling performance.

Also, note that the star rating changes in an interval of two years or so. While buying an air conditioner, make sure you that the rating period of the AC is the latest. Try to find a balance between EER and ISEER.

And yes how can we forget that more stars mean more expensive your air conditioner will be. But don’t worry about the price because, in the long run, you will end up saving a lot more in power consumption of the air conditioner.

Wrap Up

You can save electricity bill shock while running your AC by going for higher star ratings and ISEER rating. Do not forget to check this rating if you are planning to buy an air conditioner.


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