SEER Ratings Explained

SEER is a report card, a class grade. SEER stands for Seasonal Energy Efficiency Ratio, and it guides consumers to purchase the best air conditioner or heat pump for their home or business.

The Math Behind SEER
An air conditioner’s SEER number is like a car’s mpg rating: the higher, the better. It measures efficiency. How much do you get for what you put in? SEER is calculated by dividing a unit’s cooling output by its power input over a certain season of time.

Now, this sort of logic could devolve into the thickest of alphabet soups, with SEER being compared with EER and COP, all of which are based on BTUs and W*HRs. But away with the acronyms! Why not dig up a little algebra?

The marginal savings of an air conditioner decrease the higher the SEER number. If a sun-stricken customer replaces his rickety SEER-8 unit in a 3-ton system with a SEER-13 air conditioner, he will save approximately $5,000 over the lifetime of the unit. If he purchases a shiny new SEER-16 unit, however, he will save only $3,000, even though the difference between each unit is a rating of four SEER points.

So why doesn’t everyone save the cash and purchase the minimum acceptable unit?

How about a little history?

SEER in the Real World
By decree of Uncle Sam and the Department of Energy, all air conditioners sold on or after January 1, 2006, must have a minimum SEER rating of 13. Energy Star appliances must have a rating of 14. Window-mounted appliances ducked out of the law, and therefore may have a lowly rating of nine or ten.

However, the hotter the summer, the longer the season, and the more expensive the electricity, the more important it becomes to have a more efficient unit. The DOE realized this in 2011 and imposed a new rule on the Southeastern and Southwestern United States: minimum 14 SEER.

How High Can SEER Ratings Go?
By law of the Carnot thermodynamic cycle, an ideal cycle every engineer knows and loves, no air conditioner can be perfectly efficient. In the same way that no child’s swing can sway forever, no air conditioner can turn every ounce of power into work. With that said, the industry is putting up a valiant effort to the contrary.

HVAC professionals often recommend SEER-16 home air conditioner units. Some homeowners even choose SEER-rated 18 units. Yet wizards in the industry use A/C inverters and variable-speed technology to slash energy consumption by almost half, and ductless units are available with SEER ratings of 30 or more.

Why are SEER Ratings Important?
SEER ratings are little lighthouses that shine the light on good – and not so good – air conditioners. Homeowners looking to maximize their savings and minimize their carbon footprint can choose both with an appropriately rated air conditioning unit. SEER is a standard for excellence, and as mechanical magicians push the boundaries of technology, that standard will grow ever higher.


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