What is EER? Ultimate Guide to EER Rating

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What is EER

EER rating is the energy efficiency ratio of an air conditioner or heat pump. That’s what the letters stand for. But what is the EER definition? EER meaning?

The answers and much more are here.

Air conditioner and heat pump manufacturers are required to list the EER rating on their products as part of guidelines issued by the United States Department of Energy, or DOE. The information gives you the consumer the chance to compare efficiency levels for the air conditioners you are considering. Truth in advertising or full disclosure might be the way to put it.

This guide to EER definition, i.e., EER meaning covers these topics and more:

According to the Demand Institute, 71% of homeowners want an energy efficient home, but only 35% think their current home is energy efficient. In fact, that study is a few years old. We think the current number that want an energy-miser home is closer to 80%.

That’s why information about EER and EER meaning is in demand.

EER Definition or Meaning

What is EER Rating? The Energy Efficiency Ratio of an air conditioning or heat pump: EER measures how efficiently it uses electricity to remove heat from your home.

EER ratings are used for all air conditioners including window air conditioners, portable air conditioners and mini split / ductless air conditioners. Increasingly, they can be found in the literature of standard split system air conditioners.

One of the first split system AC manufacturers to list EER was Rheem, as you can see on its main Split System Air Conditioner page.

The EER rating of your air conditioner should be listed in the specifications in the owner’s guide. Or it might be found on an Energy Guide label like this one that also shows how much energy you can expect it to use and the cost given average electricity prices.

EER

How AC Works

This is a brief explanation of AC and heat pump function: Air conditioners and heat pumps have an outdoor unit that contains a compressor and radiator-like coil.

The indoor unit is a coil located in or adjoining your furnace or air handler. A set of lines circulate refrigerant between the two.

AC Mode: The compressor pumps refrigerant into your home, and it cycles through the indoor coil where it evaporates and collects heat. The refrigerant carries the heat outside, and the heat is released through the outdoor coil as the refrigerant is compressed.

The less electricity used by the unit to do the job, the more efficient it is – the higher its EER rating is.

Heat Pump Mode: The flow of refrigerant is reversed. The unit collects heat outdoors, and it is pumped inside to be released from the indoor coil to warm the air being circulated by your blower fan through the ductwork of your home.

EER rating is for air conditioning only! There is a separate rating called HSPF, or Heating Seasonal Performance Factor, for when a heat pump is in Heat Mode.

How EER Rating is Determined

EER rating is a very specific measurement.

It measures how energy efficient an air conditioner or heat pump cools when:

  • The outdoor temperature is 95 degrees Fahrenheit
  • Indoor temperature is set at 80F
  • The relative humidity is 50%

Every air conditioner and heat pump is measured under these very specific conditions that can be produced in a lab. This is the only way to compare “apples to apples;” measure each one under the same conditions.

The EER Rating Equation

Specifically, EER is defined as the number of BTUs per hour of heat moved per watt of electricity required. So:

BTU/H divided by Watts of electricity = EER

Where can I find BTU and watts for my AC?

The product specifications should include them. The BTU rating, such as 8,000 BTU/H (per hour) or 12,000 BTU, is usually listed on a metal tag on the AC or the front cover of the owner's manual or the box it arrives in.

The second figure, watts or cooling watts, should be listed too. And you can divide the BTU/h by the cooling watts to get the AC EER rating.

For example, the LG LW1817IVSM window air conditioner is an 18,000 BTU model. That means that every hour, it will remove 18,000 British Thermal Units (BTU) from the air under the EER testing conditions mentioned above. It uses 1,590 watts per hour to do this.

18,000 divided by 1,590 = 11.3 EER

LG makes outstanding window air conditioners, and you might enjoy our LG Window AC Reviews and Guide.

How does heat affect EER? If the temperature outside is hotter than 95F, then efficiency might be lower – with some exceptions. A unit will be more efficient in lower temperatures too, if humidity is the same.

How does humidity affect EER? If it is 95F outside and the humidity is higher than 50%, efficiency will be worse.

An AC runs more efficiently when the humidity is lower. For example, if air conditioners were tested at 95F outdoors, 80F indoors and 25% humidity, like you might find in Arizona, then the EER rating would be higher. The reason for this is that the more moisture there is in the air, the harder it is for the AC’s outside coil to cool as the refrigerant releases heat into it.

What does the term “ratio” mean in EER? It is the relationship between the amount of heat moved to the amount of electricity used in the process. However, EER isn’t written like a ratio. For example, the rating for a window air conditioner that is 11 EER isn’t written 11:1, just 11. It’s always assumed the reading is BTUs per 1 watt of energy.

What does AHRI mean? You might see that acronym when researching EER efficiency. It is the Air Conditioning, Heating, and Refrigeration Institute, and it has been instrumental in developing measurements like EER, SEER, COP, SCOP and other efficiency ratings.

How is EER Rating Different Than SEER Rating?

EER vs SEER is a common comparison.

EER is the EER rating; SEER adds the word “seasonal” to the beginning, so SEER is the Seasonal Energy Efficiency Ratio.

SEER is the measurement of how efficiently the air conditioner will perform over an entire cooling season. It isn’t as precise as EER and it can be misleading depending on your climate.

While EER is measured under precise conditions, the outdoor temperature and humidity vary significantly over the course of a cooling season. This can lead to inaccurate numbers. For example, a 16 SEER air conditioner might only achieve 14 SEER in hot, humid Georgia but have a performance of 17 SEER in a cooler, drier state like Minnesota.

ASM Air in California suggests that the SEER ratings are accurate if your average summer temperature high is 83F. The efficiency drops by about 1 SEER for every 5 degrees above 83 your average is.

To measure SEER, the air conditioners are tested at outdoor temperatures ranging from the mid-60s to 100F.

Who turns on the AC when it is 65F outside? Well, if it is very sunny, the home is poorly insulated and has a black shingle roof, the temperature inside the home can rise to a temperature at which some homeowners would want to turn on the AC. And some people are very averse to heat and like it really cool.

SEER ratings are only used for mini split and standard central air conditioners and heat pumps, not window/portable/wall/room air conditioners.

EER is more accurate than SEER, as you can see, because all units are rated under the same conditions. That is why EER is used for all types of room air conditioners and are starting to show up on split system air conditioner product pages too.

HVAC technicians always consider the EER of a unit when recommending AC size and efficiency to their customers.

Why is EER lower than SEER?

Simply put, they are different measurements. You can’t compare EER to SEER head to head. Apples and oranges.

What is the CEER Rating?

We get asked, “my AC has a CEER rating. What is EER vs CEER ratings?”

The answer is simple. The CEER rating stands for Combined Energy Efficiency Rating and includes how much energy the air conditioner uses while idle. When plugged in but not running, it will use a very small amount of energy.

So, CEER is higher than EER. The LG unit mentioned above has an EER rating of 11.3 and a CEER rating of 14.7.

EER Rating Chart

If you enjoy math, then you can convert SEER to EER using this equation.

eer to seer formula

However, we’ve done the math for those who don’t want to.

This EER rating chart shows common SEER and EER conversions.

It also shows how much energy and money you can save as EER/SEER increases.

EER RatingSEER RatingSavings
89.110%
99.7711%
1010.4320%
1112.5726%
1213.7133%
1314.8638%
141643%
1517.1447%
1618.2950%
1719.4353%
1820.5756%
1921.7158%
2022.8660%
212462%
2225.1464%
2326.2965%
2427.4367%

What’s the Best EER Rating? Or which AC EER Rating Do I Need?

As noted, the higher the EER rating, the more efficient the air conditioning is. However, choosing the highest EER rating isn’t always the most cost-effective choice.

The energy efficiency or EER that is best for you is determined by your climate or your commitment to green air conditioning.

In short, the hotter and more humid your climate is, the more it makes sense to choose an air conditioner with a higher EER rating than in cooler climates. It will cost more, but the lower energy bills will pay back the higher cost in 1-5 years depending on your climate and the room air conditioners you’re comparing/considering.

There aren't any mandated requirements. However, the most common recommendations are:

There’s one more factor to consider – How much you plan to run the air conditioner.

Well, of course you’ll run it more in a warm and humid climate. However, even in a muggy climate, some homeowners won’t run a window air conditioner or portable air conditioner a lot. For example, maybe you have central AC, but on the hottest days a West-facing room up upstairs bedroom gets warm – the central air conditioning can’t quite do the full job. In rooms like that, a room air conditioner used occasionally will be useful – and it doesn’t have to be a super-efficient model.

Top EER Air Conditioners

Here’s a brief list of room and window air conditioners with excellent EER ratings.

6,000 BTU model: Frigidaire Energy Star 6000 Window AC

8,000 BTU model: TOSOT Energy Star Window AC

10,000 BTU model: Frigidaire Energy Star Compact Window AC

12,000 BTU model: Frigidaire Compact Window AC

15,000 BTU model: Perfect Aire Energy Star Window AC

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