What is SEER vs. EER? Should I Care?

This is a common question, and an important one. To put the issue in perspective, ask yourself: “Do I know what MPG means when it comes to cars?” Of course! We all do. Especially since gas prices shot through the roof a number of years ago, we have all been concerned about how many miles we can get on a gallon of gas.

Well the question of “SEER vs. EER” is related since they both are measurements of an air conditioner’s efficiency. And just like higher MPG is better, higher SEER and EER ratings mean better efficiency. But why are there two measurements? Which is more important? Which one should you pay more attention to when deciding to purchase a new central air system? First things first: before discussing “SEER vs. EER” you need to understand what each of them is separately.

What is SEER?

SEER stands for Seasonal Energy Efficiency Ratio and is the most common way to evaluate the efficiency of an AC unit. Keep in mind that this only applies to cooling power not heating so SEER is not used for Furnaces or the heating cycle of heat pumps.

An air conditioner’s SEER rating is calculated by taking the average cooling output of the HVAC unit throughout a normal cooling season (measured in BTUs), and dividing it by how much energy was consumed (measured in watt-hours). SEER ratings cannot be calculated in the field on individual units. This is because they are calculated using an average of an entire cooling season, a constant indoor temperature, and varying outdoor temperatures ranging from the 60’s to over 100 degrees F, plus average US household energy expenditures.

The yellow Energy Guide Tag on all central air units will show a possible range of around 8 to 30, although since 2005 the manufacture of household AC units lower than 13 SEER has been restricted, and at the time of this writing very few air conditioning units are more efficient than about 25 SEER. But again, a higher SEER value is a more efficient cooling unit.

What is EER?

Alright, now you understand half of the SEER vs. EER question. So let’s move on to the second half. EER stands for Energy Efficiency Ratio. Sounds similar, right? And it is, but it is actually an older means of calculating energy efficiency than SEER. In 1975 the Air Conditioning & Refrigeration Institute (now known as AHRI, the “H” was added for ‘heating’) introduced the EER as the first ever universal standard of measurement for HVAC efficiency.

Like SEER, an air conditioner’s EER rating also measures the AC unit’s efficiency, but EER is more of a constant. It is calculated using the nearly the same formula but using a constant outside temperature of 95 degrees, a constant inside temperature of 80 degrees and a humidity level of 50%. So the “Seasonal” variable is not factored in.

So now you understand what SEER is and what EER is. Sound to you like it’s just splitting hairs? Well there’s a reason for having two different ways of representing the energy efficiency of a central air unit. In fact, starting in 2015 in some regions of the US, there are not just minimum SEER rating requirements, but also minimum EER rating requirements. We’re going to delve into that coming up soon. [UPDATE: Click here to read Part 2 of this article.]

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