Understanding AC Energy Ratings
If you’re in the market for a new air conditioning system, it’s helpful to understand different energy rating systems and what they mean.
The two pivotal rating methods are known as EER and SEER. The US government requires AC units to display a SEER rating, but many also include an EER rating. In both instances, higher numbers indicate more energy efficient components. Let’s take a closer look.
The Energy Efficiency Ratio (EER) rating was created in 1975 to provide an annualized measure of efficiency. While EER ratings can be useful, in practical terms they’re comparable to highway MPG. They describe efficiencies achieved under peak demand on the hottest days but they don’t address changing variables like climate, temperature and humidity.
From a technical perspective, EER ratings indicate how much cooling output is generated for every unit of energy consumed. Cooling output is expressed in BTUs and power consumed is expressed as watts. An EER rating of 12 or higher is considered excellent.
The Seasonal Energy Efficiency Ratio (SEER) rating system was developed in the late 1970s as a way to provide a standardized AC efficiency measurement based on seasonal usage. Like EER, the SEER rating is calculated by comparing the amount of cooling output generated for each watt of energy consumed, but it incorporates a broader range of factors, such as external temperatures and efficiency losses that occur as a unit cycles on or off.
SEER ratings tend to be a more accurate reflection of typical residential AC usage, in the same way that city MPG more accurately reflects a driver’s actual MPG on a day-to-day basis.
SEER ratings help indicate how energy efficiency has improved through the years. In the early 1970s, a typical HVAC unit might have an efficiency rating of 6 but by the mid-1980s, SEER 8 was common. In 1992, the federal government established SEER 10 as the minimum for split AC systems. In 2006, the standard rose to SEER 13, and in 2015 new AC units installed in some regions of the US must have a SEER 14 rating or better.
EER ratings indicate how well a system operates on the hottest days of the year. SEER ratings indicate overall efficiency and can help you estimate the cost to operate a particular unit over the course of a cooling season. For example, running a 3-ton SEER 10 unit for 2000 hours might cost about $720. In contrast a more efficient SEER 15 unit might cost about $480, which could help you save $2400 in utility expenses over a 10-year period.
The takeaway here isn’t the specific dollar amount, it’s the relative savings that can be achieved with a more efficient unit. If all other factors are equal, replacing your old SEER 10 with a SEER 15 unit could help you reduce your utility costs and cut energy consumption by about 34%.