EER: Energy Efficiency Ratio -- What is a Good EER Rating for AC?
EER, or Energy Efficiency Ratio, measures the energy efficiency of an air conditioner or heat pump. To do this, manufacturers test the unit at the outdoor cooling temperature of 95°F and then give an EER rating, typically somewhere between 11 and 14 EER.
A higher EER rating means your air conditioner is more energy efficient -- and that’s a good thing! An energy-efficient AC will save you money on your utility bills and leave a small carbon footprint in the process.
What is EER?
Like we mentioned earlier, EER is the energy efficiency of your air conditioner. EER ratings are always calculated with the AC unit working at an outdoor temperature of 95°F, an indoor temperature of 80°F, and at 50% humidity.
EER is calculated in terms of capacity and power. Capacity is measured in BTUs (or British Thermal Units) and it refers to the size of an air conditioning unit, or the amount or heating and cooling a unit can provide. Power is measured in W (or Watts), which is a standard unit of power.
To find EER from these two variables, simply divide Capacity (BTUs) by Power (W). Both metrics will be listed on your HVAC device. This makes the formula for finding EER:
BTU/W = EER
For example, if your room AC runs at 13,000 BTUs (an average amount for a moderate climate cooling season) and uses 1,000 watts of energy, EER would be calculated by:
EER = BTU/W
EER = 13,000/1,000
EER = 13 (a very energy-efficient AC unit!)
EER vs. SEER
EER and SEER both evaluate an air conditioner’s energy efficiency, but they’re concerned with two different types of temperature conditions:
- EER measures an air conditioner’s efficiency at the peak cooling temperature of 95°F.
- SEER, or Seasonal Energy Efficiency Rating, measures an air conditioner’s efficiency throughout an entire cooling season, with temperatures ranging from 65°F to 104°F.
Think about SEER as being an average of AC efficiency, while EER is one specific data point. You can expect Trane’s product descriptions to include SEER rather than EER. Because EER reflects specific conditions, it may not apply to some homeowners. SEER is more widely applicable and is often more meaningful than EER to a larger group of AC owners.
Minimum SEER ratings are 14 in the United States for heat pumps and air conditioners in the South, and 13 for air conditioners in the North. Minimum EER ratings vary based on tonnage and range anywhere from 11.7 to 12.2 for air conditioners in the Southern U.S., with no minimums in other areas of the U.S. and no minimums for any heat pumps nationwide, according to the Department of Energy.
When does understanding EER matter?
While understanding EER is important for all AC unit owners to get the full picture of their unit’s efficiency, understanding EER is especially important if you live in the Southern United States or a state like Arizona or Florida, where high, humid temperatures are the norm.
EER ratings are typically more important for those living in the Southern U.S. because EER is calculated by using one temperature -- 95°F. In the South, it’s pretty standard for summer days to reach and exceed this high temperature, so EER is crucial in understanding how your air conditioner will hold up during hot days. In the North, such high temperatures aren’t as common, so a rating of how energy efficient your AC unit is at this high degree isn’t going to be too useful for you.
If a unit has a really high SEER, but a really poor EER, it means it’s really efficient in mild and cool conditions, but has poor efficiency when it's really hot. This is very important for homeowners who live in extreme temperatures to understand, so you can get a unit that best suits your lifestyle!
What’s a good EER rating for an air conditioner?
According to the Department of Energy, minimum EER ratings for air conditioners range anywhere from 11.7 to 12.2 in the South, depending on tonnage. But, these are just minimums and if your unit is significantly better than those government-mandated numbers, it will earn an ENERGY STAR-certified EER rating.
ENERGY STAR-rated units come with many benefits for homeowners: they indicate your unit has an excellent EER rating, is made with better materials, and has a significantly less harsh impact on the environment. ENERGY STAR rated air conditioners must have EERs of 12 for split-system air conditioners and 11.5 for packaged air conditioners. Starting Jan.1, 2022, these ENERGY STAR minimums will be raised to 12.5 for split system air conditioners and 12 for packaged air conditioners.
Heat pumps have ENERGY STAR requirements, too. ENERGY STAR minimums are 12 for split system heat pumps and 11.5 for packaged heat pumps. These minimums will also increase on Jan. 1, 2022, bringing them up to 12.5 for split system heat pumps and 12 for packaged heat pumps.
|CAC Split Systems||≥ 15.2||≥ 12.0|
|CAC Single Package Equipment*||≥ 15.2||≥ 12.0|
Allowable prior to January 1, 2022
|CAC Split Systems||≥ 16.0||≥ 12.5|
|CAC Single Package Equipment*||≥ 16.0||≥ 12.0|
|HP Split Systems||≥ 15.2||≥ 12.0||≥ 7.8|
|HP Single Package Equipment*||≥ 15.2||≥ 11.5||≥ 7.2|
Allowable prior to January 1, 2022
|HP Split Systems||≥ 16.0||≥ 12.5||≥ 9.2|
|HP Single Package Equipment*||≥ 16.0||≥ 12.0||≥ 8.5|
Source: ENERGY STAR
Why does choosing a high EER-rated AC matter?
Owning a high EER-rated air conditioner helps both you and the world around you! If every room air conditioning unit sold was ENERGY STAR-certified, consumers would save over $350 million collectively each year and greenhouse gas emissions would be reduced by 6 billion pounds annually, reports ENERGY STAR.
Plus, homeowners with ENERGY STAR-rated AC units may be eligible for a government tax credit of up to $300. You can fill out an application online through the IRS for this credit, as long as your AC unit is in your existing home, which you must also use as a primary residence.
Theoretical EER Calculator
Each air conditioner has its own EER rating, all of which are measured at the conditions of 95°F (outside), 80°F (indoor), and 50% humidity.
Theoretical EER is the potential EER of a perfect air conditioner, in your ideal weather conditions. The formula for theoretical EER includes coefficient of performance (COP), which measures the relationship between power drawn out of an HVAC device and the power supplied to that HVAC device. To do this, you use the hypothetical temperature outside as Thot and the hypothetical desired temperature you want inside your home as Tcold. Both of these numbers are expressed in degrees Kelvin (K) instead of degrees Fahrenheit (F).
This makes the formula for COP: Tcold/(Thot - Tcold) = COP
Using the metric of COP, and the number 3.41 (because that’s the amount of BTUs in every kilowatt-hour of energy) the formula for theoretical EER becomes:
Theoretical EER = 3.41 x COP
For example, say it was 90°F outside (Thot) and you want your room to be 75°F (Tcold). To calculate the theoretical EER for this, first convert 90°F to 305K and 75°F to 297K. Then:
Theoretical EER = 3.41 x (Tcold/(Thot - Tcold))
Theoretical EER = 3.41 x 297K / (305K - 297K)
Theoretical EER = 3.41 x (297K / 8K)
Theoretical EER = 3.41 x 37.125
Theoretical EER = 126.6
This means, if a room air conditioner was cooling perfectly at these temperatures, it’s EER could be up to 126.6!
A high EER rated air conditioner could save you money on your utility bills and help the environment in the process. If you’re looking to purchase or upgrade a room air conditioner, Trane can help.