As we all know, air conditioners are one of the most power consuming home electronics and we are always looking for AC that consumes less power while giving good cooling. Thanks to ratings such as ISEER and EER, you can easily know how much power an AC consumes, so you can pick the right one.

These are the two main ratings that are being used in India to determine the power saving ability of any air conditioner.

However, both these ratings are often confused with one another. Even though they both talk about the power saving ability of an AC, they are not the same and use different methods of calculation to do so.

ISEER uses star ratings, the more stars an AC gets, the less power it will use. However, EER uses numbers to show the power usage, the higher the number, the lesser power it will consume.

Not just this, there are many other things you need to know about ISEER and EER. So, in this article, we have explained in detail what both of these ratings mean along with their pros and cons. Stay till the end for some additional FAQs related to the AC ratings.

What is the ISEER Rating?

ISEER stands for Indian Seasonal Energy Efficiency Ratio. It is a new method of calculating the energy efficiency of an air conditioner in the Indian market.

This method was started in 2016 and it rates the energy efficiency of an AC by awarding them stars. As we already said, the more stars an AC has, the higher its energy efficiency is.

Why is ISEER Rating Important?

Unlike other countries, in India the temperature changes drastically from one season to another. This causes the usage and electric consumption of an AC to fluctuate drastically as well.

So, the BEE (Bureau of energy efficiency) decided to take into consideration all these factors and created a separate rating system that is known as the ISEER rating.

It can be defined as the ratio between the total amount of heat removed by an AC to the total energy consumed to do so in a year.  Here, the assumption is that the AC is operating continuously in active mode.

How is ISEER Calculated?

The simplest way to calculate ISEER is heat removed/ energy consumed.

This is written as,


CSTL stands for Cooling Seasonal Total Load which represents the total heat removed while operating in active mode for a particular period of time.

CSEC stands for Cooling Seasonal Energy Consumption, which measures the total energy used by the AC while operating in active mode for a particular period of time.

Assumptions: In order to calculate this ISEER ratio, certain assumptions are made. These are;

  • The AC is operating continuously in active mode
  • The air conditioner operates for 1600 hours (2 months) per year
  • The temperature of the environment is an average of 54 Indian cities

The Benefit of an ISEER rating:

  • This is more suitable for Indian weather conditions and Indian household air conditioner usage.
  • The rating gives you an idea about the power saving ability of an AC and you can estimate your electricity bill accordingly.
  • Get rebates and incentives for using energy efficiency and eco-friendly products.

What is the EER rating?

EER stands for Energy Efficiency Ratio. This is a standard way to calculate energy efficiency that is primarily followed in the US. The original version of ISEER and was used to rate the energy efficiency of AC in India before ISEER.

Here, the ratio is calculated between the heat removed from the room per hour divided by the power consumed during the hour. Here also, the higher the EER, the more efficient the AC is.

How Do you Calculate EER?

EER is calculated as,

Cooling capacity in BTU/ power consumption in Watts

Assumptions: The EER makes some assumptions regarding the interior and surrounding temperature. These are,

  • The temperature inside the room is 27 degrees
  • The temperature outside is 37 degrees
  • The humidity level is 50%

Benefits of EER

  • The EER can accurately measure the energy efficiency of an AC
  • This is the most accurate method to compare two or more ACs to determine which one performs better in terms of energy efficiency.
  • Works well for areas where the temperature remains relatively similar throughout the year.


The main difference between ISEER and EER is that EER assumes that temperature remains the same throughout the year. This is an incorrect assumption as the temperature and humidity level will change according to seasons and area of operation. The ISEER takes this into account while calculating the ratio.

The ISEER is also represented in stars to make it easier for users to determine the energy efficiency of a device whereas the EER rating is represented in numbers which might get confusing for users.

ISEER is a better way to evaluate the energy efficiency of an AC whereas it is widely believed that EER is better while comparing two or more ACs to compare their energy efficiency.


1. Why is EER called ISEER?

Ans: EER is a standardized method to calculate the energy efficiency of an AC, this assumes a constant temperature and weather condition throughout the year.
The ISEER as we stated above is a modified version of the EER that takes into account the variations in temperature and weather conditions throughout the year. This rating is formulated to customize it according to Indian household usage and weather conditions.

2. What is the basic difference between ISEER and BEE ratings for an AC?

Ans: BEE stands for Bureau Of Energy Efficiency is an agency that is the regulating authority that decides the ISEER ratings for all ACs in India.

3. How do you read an EER rating?

Ans: The EER rating is calculated by dividing cooling capacity/ power consumption. So, all you need to do to find out the energy efficiency is that the higher the EER the better efficiency an AC has in terms of energy consumption.
You can also use this formula to find out the power consumption or the cooling capacity individually.
EER= cooling capacity in BTU/ power consumption in Watts
Cooling capacity = power consumption X EER
Power consumption = Cooling capacity/EER

4. What is EER in HVAC?

Ans: In simple language, EER is the rating that indicates the energy efficiency of an HVAC device. This is calculated as the ratio between the cooling capacity in BTU and power consumption in Watts.


While EER and ISEER are both great at calculating the energy efficiency of an HVAC device. The accuracy will vary according to the area you live in. If you live in India with its fluctuating temperature and weather conditions then you should rely on the ISEER ratings for accuracy rather than the EER ratings.

But if you want to know the energy efficiency of the AC in itself or compare it to other ACs then the EER ratings should be your preferred rating.