Both EER and SEER ratings are metrics that determine the energy efficiency of an air conditioner. Since they measure the same thing, we’ll see how they differ in EER versus SEER observations.

*Example:* All in one mini split air conditioner. It happens **19 CER Rating** And a **12.7 EER Rating**, what does this mean?

First, let’s look at what EER and SEER are and how they are defined:

**EER**stands for, It is calculated by dividing the AC cooling output (in Btu/hr) by the maximum wattage of the air conditioner. EER is used to denote the theoretical energy efficiency of portable AC units and window AC units.**I**energy**I**efficiency**R**very**seer**stands for, It is calculated as the weighted average of the various EER ratings (EER.)**s**easy**I**energy**I**efficiency**R**very_{25%}EER_{50%}EER_{75%}and EER_{100%}) SEER is used to denote the practical energy efficiency of mini split air conditioners and central aircon systems. was introduced in 2008 ANSI/AHRI Standard 210/240 Instructions,

Here is the main difference between SEER and EER ratings:

EER rating a . More than *theoretical measure* of energy efficiency of AC. SEER aims to more adequately achieve practical energy efficiency of air conditioners during the summer.

In short, the EER rating formula is a simple calculation. To calculate an air conditioner’s EER rating, we divide the cooling output by the maximum AC wattage, like this:

Cooling output is measured in certain EER test conditions: outdoor temperature of 95°F, indoor temperature of 80°F, and 50% relative humidity.

This is a theoretical calculation. In practice, however, we use air conditioners at different outdoor and indoor temperatures and at different relative humidity levels.

to best capture **realistic conditions**AHRI has introduced SEER rating. The SEER rating is calculated as the weighted average of the various EER ratings. To illustrate this, the SEER formula is:

Let’s quickly explain what all this weighted average SEER rating means. We will first look at the EER rating and then compare the EER rating with the SEER rating. We will also show you how to easily convert EER to SEER and SEER to EER:

### Explanation of EER Rating

The EER rating is the simplest possible measure of an air conditioner’s energy efficiency. SEER rating is basically a practical derivative of EER rating. It is important to understand that EER is measured by **Specific** Tested conditions by AHRI (Air Conditioning, Heating and Refrigeration Institute).

AHRI tests portable and window air conditioners:

- 95°F outdoor temperature.
- 80 degrees Fahrenheit indoor temperature.
- 50% relative humidity level.

This means that we run these room AC units at these temperatures and relative humidity. To calculate the EER rating, we only need to measure two metrics, namely:

- power input. This is the electrical power that we use to generate the cooling output. The AHRI Bus Test measures the maximum wattage of the AC on the conditioner. You do this with a watt-meter.
- cooling output. It is a measure of how much cooling capacity we get from a room AC unit with the measured power input under EER test conditions.

Based on these two metrics, we calculate the EER rating using this formula:

Example: We are testing a portable air conditioner at test conditions (95°F, 80°F, 50% humidity). The maximum wattage the unit runs on is 1,000W. Now we measure that when the AC is running at 1,000W the total cooling output is 12,000 BTU/hr. Basically, we have a 12,000 BTU air conditioner. Here’s how the EER rating is calculated:

**EER Rating** = 12,000 BTU/hr = 1,000 W **12**

That means we have 12 EER rated air conditioner. To get an idea of what a good EER rating is for an air conditioner, here are the average EER ratings for room AC units:

- Portable air conditioners have an average EER rating of around 8.5 EER.
- The average EER rating of window air conditioners is around 10 EER.
- The average EER rating of a through-the-wall air conditioner is about 9 EER.

Now, in the real world and during the summer, we don’t always have a 95°F outside temperature. Nor do we always have an 80°F indoor temperature. Of course, the relative humidity level isn’t even 50%.

At different temperatures and relative humidity, air conditioners will have different performances. In short, the EER rating test conditions are perfect conditions. If you measure the energy efficiency of an air conditioner at 110°F outdoor temperature, 78°F indoor temperature, and 60% relative humidity, the energy efficiency will drop.

This also means that the standard EER rating is not so much a measure of how well an AC unit will perform under actual conditions…

…but there is a SEER rating.

The whole point of why the SEER rating was introduced is to better estimate the energy efficiency of an air conditioner under realistic summer conditions.

## SEER vs EER Rating

The goal of the SEER rating is to more accurately estimate the energy efficiency and thus cooling costs of the EER rating.

To achieve this, additional tests are performed while measuring the SEER rating. The EER rating is normally measured at 100% wattage (full load EER). It’s EER. as shown_{100%} In the SEER equation:

In addition, EER_{100%}AHRI measures the energy efficiency of an air conditioner at 25% wattage (EER.)_{25%}), 50% Wattage (Eer.)_{50%}), and 75% wattage (Eer.)_{75%}) as well. These are known as partial load EER ratings.

The final SEER calculation is the weighted average of these 4 different EER measurements.

To illustrate how SEER is calculated based on these 4 EER measurements, let’s look at an example:

Let’s say we have a 12,000 BTU air conditioner with the 12 EER rating from the previous example. Here are theoretical measurements of energy efficiency at 25%, 50%, 75% and 100% wattage:

- 4,000 BTU at 25% load (250W). This gives 16 EER. Get
_{25%}rating. - 7,500 BTU at 50% load (500W). This gives 15 EER. Get
_{50%}rating. - 10,500 BTU at 75% load (750W). This gives 14 EER. Get
_{75%}rating. - 12,000 BTU at 100% load (1,000W). This gives 12 EER. Get
_{100%}rating.

With these partial and full EER weights, we can calculate the SEER rating. Let’s plug all these metrics into the SEER equation:

**watcher rating** = (1×12 + 42×14 + 45×15 + 12×16) / 100 = **14.67 ser**

As we see, we get an EER vs SEER ratio of 12 vs 14.67. In general, the SEER rating is always higher than the full load EER rating.

The SEER rating measures seasonal energy efficiency sufficiently for EnergyGuide to estimate annual expected running costs based on the SEER rating.

Now, in many cases, we need to convert EER to SEER and SEER to EER.

For this purpose, we can use 2 equations.

*Equation 1:* Here is a simplified equation that you can use to find a low SEER rating (below 14 SEER).

**EER = 0.875 × SEER** And **seer = 1.143 × EER**

Example: We had 12 EER rated AC units. SEER is calculated as follows:

**seer **= 1.143 × 12 EER =**13.72 **

We see that this equation does not give us the exact EER vs SEER conversion. However, it is a good approximation. You can read more about how to convert SEER to EER here.

For a more accurate calculation, we need to use Equation 2.

*Equation 2:* This is a more complex but more accurate SEER vs EER calculation.

**EER = -0.02 × ser² + 1.12 × ser**

We have explained in this article how to convert EER to SEER accurately.

With all this in mind, hopefully, you now have a better understanding of some of the complex differences between EER and SEER ratings.

You can also read here what specifically means EER rating and what is meant by SEER rating. Both of these articles include cost-savings calculators in US dollars.

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