What is EER2: EER vs EER2

EER and EER2 are energy efficiency ratings used for all air conditioning units and systems. They are used in setting standards like the minimum Energy Efficiency Standards for the heating and air conditioning industry.  

Basic idea: EER and EER2 are measurements of how efficiently air conditioning equipment uses electricity to produce cooling – i.e., the removal of heat from air.

Old: EER is an outdated rating. EER stands for energy efficiency ratio (not rating). It’s that simple.

New: EER was replaced by EER2 on January 1, 2023. However, you’ll see both ratings still in use as the industry switches over to the new rating.

This page defines the terms and explains their use and how they are different – and also discusses the difference between EER2 and SEER2.

What is EER2?

EER2 meaning is simple – it is the replacement rating for EER. The second version. EER 2.0.

EER2 is new for 2023.

What does EER2 measure?

What EER2 measures is the ratio of BTUs of heat removed from the air relative to the amount of electricity consumed by the equipment. The energy used is measured in watt-hours.

How is EER2 calculated?

To start with, it will be useful to understand how the old rating EER is calculated. From there, we can discuss how the EER calculation is adjusted to produce the EER2 efficiency ratio.

The Basic EER and EER2 Calculation

The first calculation for EER and EER2 is simple: The BTU capacity of an air conditioner is divided by the watts it consumes.

The Department of Energy definition for EER2 follows, but it applies to the first calculation needed for EER too: “EER2 is the ratio of the average rate of space cooling delivered to the average rate of electrical energy consumed by the air conditioner or heat pump. This ratio is expressed in Btu per Wh (Btu/Wh).

This gives an efficiency rating – the ratio expresses the heat removed compared to the energy consumed.

Example: Consider 2 ACs, both 18,000 BTU, aka 1.5 tons.

Model 1: Uses 1,300 watts. 18,000 BTU / 1,300 Watts =  13.8 EER efficiency.

Model 2: Uses 1,700 watts. 18,000 / 1,700 = 10.6 EER efficiency.

The first model has a higher rating, which means that it removes more BTUs of heat for each watt of energy it consumes during the process.

Note: In order to produce uniform ratio data, all units are tested under the same conditions: 95F outdoor temperature; 80F starting indoor temperature; 50% RH (relative humidity).

So, how is EER2 calculated?

EER2 is calculated the same way as EER with one important difference – The testing is done using greater external static pressure, 0.1 inches of water in the water column for EER, and 0.5 inches of water in the water column for EER2.

*Inches in water column is commonly written as “in. WC”.

The external static pressure, or ESP, is the pressure of the air leaving the AC equipment with the use of a blower fan. The higher the in. WC., the more difficult it is to cool the air.

And .5 in. WC is 5 times greater than .1 in. WC. However, the US Department of Energy instituted the new EER2 testing and rating because it better reflects the actual conditions that air conditioning equipment works under.


Because EER2 is calculated using harsher cooling conditions than those used to determine EER, the ratios are understandably lower.

What is the difference between EER and EER2?

The difference is approximately 4.1% – EER2 ratings are 4.1% lower than EER ratings because of the more difficult working conditions.


20 EER = 19.2 EER2

17 EER = 16.3 EER2

14 EER = 13.4 EER2

The 4.1% number reflects how much harder an AC system works at 0.5 in. WC vs 0.1 in. WC. And that is how much more energy is required by the AC under the harsher but more realistic conditions.

Using the 18,000 BTUs AC examples from earlier, this is what energy consumption looks like under the 0.5 in. WC conditions:

Model 1: Uses 1,300 watts at .1 in. WC. It uses 1,353 watts at .5 in. WC.

As a result, the EER of 13.86 becomes an EER2 of 13.3.

Model 2: Uses 1,700 watts when tested at .1 in. WC. for an EER of 10.58. With .5 in. WC, the EER2 is just 10.17. And it requires 1,770 watts of electricity per hour.

Tip: To convert EER to EER2, follow these steps on a calculator.

1. Enter the EER rating. Use 11.5 for an example. 

2. Choose the Subtract key

3. Enter 4.1 (but don’t hit enter or the = key). 

4. Choose the % key. The number 0.4715 might appear (which is 4.1% of 11.5)

5. Hit Enter or =, and the new number shown is the EER2 rating. For this example, it is 11.0285.

What is a Good EER2 Rating?

An EER2 rating above 9.5 is considered a good EER2 rating.

You’ll find EER2 ratings this high in mini split ACs, standard split system ACs and some window air conditioners.

*No portable air conditioners come close to meeting this efficiency level.

To be a certified Energy Star air conditioner, here are the EER2 minimum standards. They are different based on equipment type:

Central split system air conditioners including mini split systems:

AC-only: Greater than or equal to 12.0 EER2.

Heat Pump: Greater than or equal to 11.7 EER2.

Packaged units (AC and blower in one cabinet):

AC-only: Greater than or equal to 11.7 EER2

Heat Pump: Greater than or equal to 10.6 EER2.

If your AC meets minimum efficiency to be Energy Star certified, you can be sure that your system has a good EER2 rating.


Remember, EER2 meaning is the energy efficiency ratio version 2.

Similarly, SEER2 is the new version of the SEER rating, which stands for seasonal energy efficiency rating. The key difference is the first word – Seasonal.

The key to understanding EER2 vs SEER2 is to know how the ratings are measured.

SEER2 is measured in conditions that reflect the changing conditions during the cooling season from spring to fall.

EER2 is measured in conditions that reflect a single set of conditions – 95F outdoors, 80F indoors and 50% relative humidity.

SEER2 is seasonal efficiency. EER2 is a single snapshot of efficiency.

Trane describes SEER2 vs EER2 this way, “Think about SEER2 as being an average of AC efficiency, while EER2 is one specific data point.”

Trane ACs are listed with the SEER2 rating, as are those from most manufacturers of central AC systems, saying “You can expect Trane’s product descriptions to include SEER2 rather than EER2, because…SEER2 is more widely applicable and is often more meaningful than EER2 to a larger group of AC owners.”

Is EER2 better than SEER2?

Yes, in hot regions like the South, the EER2 is more applicable. This is because the EER2 test is done in conditions with 95F degree outside temperature.

When summer temperature varies more, then SEER2 is a useful rating.

What is the minimum EER2?

There is a minimum EER2 for the Southwest US region only – the hottest region in the US. It is 12.2 EER2 for units less than 45,000 BTU and 11.7 for larger AC equipment. The Southwest Region is Arizona, New Mexico, Nevada and California. 


Note that all other regions have new minimum standards too, but just not for EER2, since extreme heat isn’t as common.

The Southeast is hot too! It is a little surprising that the Southeast doesn’t have new minimum EER2 standards. But it might be useful to know that these new DOE minimum efficiency standards were negotiated between the DOE and manufacturers. This might have been a compromise.

New Efficiency Ratings for 2023

One way in which SEER2 and EER2 are the same is that both are new measurements that went into effect January 1, 2023.

A new heating efficiency known as HSPF2 replaced the old HSPF. 

Written by

Rene has worked 10 years in the HVAC field and now is the Senior Comfort Specialist for PICKHVAC. He holds an HVAC associate degree and EPA & R-410A Certifications.
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