The Seasonal Energy Efficiency Ratio

Modern HVAC systems have focused on becoming energy-efficient to meet the demands of consumers who no longer want their bills to be so high. When purchasing any new system, it’s important to learn as much information as possible about each appliance to ensure that it is not only energy efficient, but also suited to the preexisting HVAC system. One of the simplest measurements is the seasonal energy efficiency ratio.

What Is the Seasonal Energy Efficiency Ratio?

SEER, or seasonal energy efficiency ratioThe seasonal energy efficiency ratio, or SEER, is a calculation through which an individual can determine how energy-efficient their HVAC system is. The higher the final number is, the more efficient the system is. It is determined by dividing the average cooling output of a system by the average energy expended during that time.

The SEER is best understood as being a maximum efficiency rating for when the entire HVAC system is functioning properly. It is similar to the average miles per gallon (mpg) a vehicle possesses.

The SEER is strongly related to the theories of thermodynamics. Thermodynamics is one of the most significant branches of physical science and has to do with the study of heat and its relationship to other forms of energy. Heat itself is understood as a form of energy and is necessary to make a functioning HVAC system and air conditioner.

When calculating the SEER, an individual is responsible for understanding how energy is used over a period of time to generate cooled air. Some of the most common units to see are British thermal units (BTUs) and watts. A British thermal unit is the amount of energy required to heat a single pound of water by 1 degree Fahrenheit. The actual amount is 1,055 joules, which would be the equivalent of 252 calories of energy for a living organism.

A watt, meanwhile, is a unit of power utilized by the International System of Units. It is essential for understanding the basics of thermodynamics and often electrical energy in general. It is the equivalent of 1 joule per second.

A joule is one of the smallest units of energy, which is why it is often used in the calculation of much larger units. It is best understood as the amount of energy transferred to an object when a single force of 1 newton acts on an object over the distance of 1 meter. When calculating the SEER, it is impractical to use joules because higher levels of energy are required to quantify the output of a basic air conditioning unit.


How to Calculate Your SEER

One of the most important steps to utilizing and understanding SEER is being able to calculate the ratio. SEER is measured in BTUs. To perform the calculation, an individual needs to know the BTUs per hour and watts per hour of their air conditioner. They need to calculate average use of the air conditioner over the summer in both units. The simplest way to do so is to multiply both units by 1,000 hours, the average time an air conditioner spends in operation during late spring and summer.

The equation will be: BTUs x 1000 and watts x 1000.

Once both of these numbers have been calculated, the SEER can be determined through the following equation: (BTUs x 1000)/(watts x 1000) = SEER.

Here is an example of the calculations using the following sample numbers:

BTUs = 7,500

Watts = 3,500

(7,500 x 1,000) = 7,500,000

(3,500 x 1,000) = 3,500,000

7,500,000/3,500,000 = SEER Rating 2.14


SEER’s Relation to EER and COP

When discussing SEER, it is common to hear similar acronyms such as EER and COP. The energy efficiency ratio (EER) of any cooling device is received by calculating the ratio of output cooling energy to input electrical energy. The ratio is determined at any operating point and is an essential term that allows individuals to see just how energy-efficient their HVAC system is.

When calculating the ratio, it is common to assume an outside temperature of 95 degrees Fahrenheit and a return air (or interior) temperature of 80 degrees Fahrenheit. Relative humidity is also averaged to 50%, even in notably wet and dry climates.

Similar to the SEER, the EER has its basis in thermodynamics and is related to the COP, or the coefficient of performance. The main difference between the EER and COP is that the calculated COP of any cooling device is designed to be without units. This is because the assigned numerator and denominator are expressed using the same units, avoiding the mixed units utilized by the SEER and EER.

The downside to using mixed units for the SEER and EER is that there is no immediate physical sense to either number. While the ratios produced are beneficial for determining overall machine energy efficiency, they cannot be quantified as they lack a central unit of measurement. For this reason, obtaining a physical example of the EER is done by multiplying the COP or EER by the conversion factor from BTU/h to watts. This conversion factor is expressed as EER = 3.41214 x COP.

The SEER is another form of the COP (or EER) expressed in units, but is not a single operating condition. Rather, it is an expected overall performance or average performance of an air conditioning unit in a specific region. Because the SEER is designed to be an average, it is calculated with the same interior temperature of 80 degrees Fahrenheit, but it has a range of exterior temperatures. One downside to using the SEER rather than the EER is the lack of allowance for different climates. However, this means the EER can be used to show how energy efficiency is affected by a variety of exterior temperatures as any given season cools.

So, this means the SEER is the COP or EER expressed in BTU/hr/W, but it has been slightly adjusted to compensate for a range of weather conditions. The EER, meanwhile, will only be for a single stagnant condition, and the COP is the physical manifestation of the ratios once assigned actual units and a method of measurement. In other words, the SEER shows how efficient an air conditioner would be throughout a season, while the EER is for specific weather conditions.

If someone knows the SEER of their unit, they are able to calculate the EER. For the majority of central residential cooling units, the EER will be equal to 0.875 x SEER. The SEER will almost always be a higher value than the EER for the same piece of equipment. So, an individual trying to measure the energy efficiency of their air conditioner should almost always be able to generate an SEER that is proportionally larger than the EER.

Individuals interested in converting SEER to EER can use the following formula:

EER = -0.02 × SEER² + 1.12 × SEER

Unfortunately, the formula does not work for all climates, particularly those that are extremely hot or cold.


US SEER Standards

The United States government became invested in the energy efficiency of residential and commercial HVAC systems beginning in 1987. Before that period, companies were able to manufacture their own range of products depending on industry technology. In 1987, legislation was passed, and it went into effect in 1992.

This first piece of legislation determined that all air conditioners needed to meet a minimum SEER rating of 10. Residents were not responsible for immediately replacing their aging units but did need to buy more energy-efficient models once the original air conditioner broke. The legislation also recommended that homeowners replace older equipment before putting their house on the market.

As technology continued to advance, the United States government chose to once again revise the standards placed on new HVAC equipment. In 2006, the required SEER rating became 13. Concessions were made to accommodate units designed to be more affordable for the average homeowner, as not all demographics would be able to purchase high-quality equipment that met the federal standards. A new number was created for air conditioners to be considered Energy Star rated. Those units needed to have a SEER of 14.5.

In 2011, the US Department of Energy (DOE) decided to revise energy conservation rules to better accommodate the wildly varying climates in different parts of the United States. Beginning January 1, 2015, new split-system air conditioners were introduced for southern and western states. The requirements for these units are 14 SEER and 12.2 EER. Any split-system air conditioner installed outside of the southern and western United States needs to meet a minimum of 13 SEER.

It should be noted that the US SEER standards are designed to be manageable. The majority of HVAC manufacturers in the American market are capable of producing more efficient models with higher SEER and EER because of continuing technological development in the field.


Current Maximum SEER Ratings

As of 2020, the highest attainable SEER rating is 42. These air conditioners tend to be mini and ductless, and therefore not practical for the majority of residential homes. In fact, the highest numbers attained by a ducted central system are almost always 10-20% lower than the SEER of a ductless model. This is to accommodate for energy that is lost through the transmission of air via pathways.

When it comes to ground-source AC units, some models are able to reach a total SEER rating of 75. In these systems, the entire HVAC system is based on the temperature of the ground or water source on which the HVAC is reliant. So, energy efficiency can vary wildly depending on temperature fluctuations, especially in a region with a varying climate.

At the same time, the SEER ratings do not accommodate the energy required to operate the pumps associated with ground-source air conditioners, meaning energy is used but not incorporated into calculations. This can create misinformation and misleading numbers, even if the intent is still good.


Why SEER Matters

SEER is significant when it comes to determining whether or not a residential property is energy-efficient. When an air conditioning unit is operating with any rating under 13, it is considered inefficient and also does not meet the baseline for equipment in the United States. This means energy is being wasted and the homeowner could be paying for extraneous use of energy.

Before purchasing any form of air conditioner, it is important to ensure that it meets basic energy standards. Individuals interested in spending less money over an extended period of time should search for a unit that has a higher SEER ranking.

It can be difficult to determine the ranking of an air conditioner when someone has not seen it in use, which is why the majority of manufacturers are required to list either the SEER or the EER of the product on the appliance itself. It can often be discovered on a large black and yellow sticker placed on the side of the device. If only one ratio is present, then the calculations shown in this article make it possible to determine the opposite ratio with little effort.



Knowing the seasonal energy efficiency ratio of any air conditioner is essential when it comes to making informed decisions about HVAC systems. As sources of energy like coal and petroleum decline, it has become more important for the average individual to focus on making conscious, energy-efficient choices for their own home.

There are numerous equations available to simplify calculations, including the following:

(BTUs x 1000)/(Watts x 1000) = SEER

EER = -0.02 × SEER² + 1.12 × SEER

Meanwhile, the COP is best understood as a stagnant number that does not require calculation.

It is possible that the ongoing demand for more renewable sources of energy will help reduce the SEER requirements of air conditioners, but it is unlikely. At the moment, the government of the United States remains focused on trying to ensure less energy is wasted during the production of cooled air. This costs less for the consumer, but also puts a smaller strain on potentially struggling urban infrastructure.

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